Theoretical exploration of Josephson Plasma Emission in Intrinsic Josephson Junctions
Tachiki, M.; Machida, M.
2000-07-18
In this paper, the authors theoretically predict the best efficient way for electromagnetic wave emission by Josephson plasma excitation in intrinsic Josephson junctions. First, they briefly derive basic equations describing dynamics of phase differences inside junction sites in intrinsic Josephson junctions, and review the nature of Josephson plasma excitation modes based on the equations. Especially, they make an attention to that Josephson plasma modes have much different dispersion relations depending on the propagating directions and their different modes can be recognized as N standing waves propagating along ah-plane in cases of finite stacked systems composed of N junctions. Second, they consider how to excite their modes and point out that excitations of in-phase mode with the highest propagation velocity among their N modes are the most efficient way for electromagnetic wave emissions. Finally, they clarify that in-phase excitations over all junctions are possible by using Josephson vortex flow states. They show simulation results of Josephson vortex flow states resonating with some Josephson plasma modes and predict that superradiance of electromagnetic field may occur in rectangular vortex flow state in which spatiotemporal oscillations of electromagnetic fields are perfectly in-phase.
Electric Field Effect in Intrinsic Josephson Junctions
NASA Astrophysics Data System (ADS)
Koyama, T.
The electric field effect in intrinsic Josephson junction stacks (IJJ's) is investigated on the basis of the capacitively-coupled IJJ model. We clarify the current-voltage characteristics of the IJJ's in the presence of an external electric field. It is predicted that the IJJ's show a dynamical transition to the voltage state as the external electric field is increased.
TOPICAL REVIEW: Intrinsic Josephson junctions: recent developments
NASA Astrophysics Data System (ADS)
Yurgens, A. A.
2000-08-01
Some recent developments in the fabrication of intrinsic Josephson junctions (IJJ) and their application for studying high-temperature superconductors are discussed. The major advantages of IJJ and unsolved problems are outlined. The feasibility of three-terminal devices based on the stacked IJJ is briefly evaluated.
Intrinsic Josephson Junctions with Intermediate Damping
NASA Astrophysics Data System (ADS)
Warburton, Paul A.; Saleem, Sajid; Fenton, Jon C.; Speller, Susie; Grovenor, Chris R. M.
2011-03-01
In cuprate superconductors, adjacent cuprate double-planes are intrinsically Josephson-coupled. For bias currents perpendicular to the planes, the current-voltage characteristics correspond to those of an array of underdamped Josephson junctions. We will discuss our experiments on sub-micron Tl-2212 intrinsic Josephson junctions (IJJs). The dynamics of the IJJs at the plasma frequency are moderately damped (Q ~ 8). This results in a number of counter-intuitive observations, including both a suppression of the effect of thermal fluctuations and a shift of the skewness of the switching current distributions from negative to positive as the temperature is increased. Simulations confirm that these phenomena result from repeated phase slips as the IJJ switches from the zero-voltage to the running state. We further show that increased dissipation counter-intuitively increases the maximum supercurrent in the intermediate damping regime (PRL vol. 103, art. no. 217002). We discuss the role of environmental dissipation on the dynamics and describe experiments with on-chip lumped-element passive components in order control the environment seen by the IJJs. Work supported by EPSRC.
Emission of terahertz waves from stacks of intrinsic Josephson junctions.
Gray, K. E.; Koshelev, A. E.; Kurter, C.; Kadowaki, K.; Yamamoto, T.; Minami, H.; Yamaguchi, H.; Tachiki, M.; Kwok, W.-K.; Welp, U.; Materials Science Division; Izmir Inst. of Tech.; Univ. Tsukuba; Univ. Tokyo
2009-06-01
By patterning mesoscopic crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (BSCCO) into electromagnetic resonators the oscillations of a large number of intrinsic Josephson junctions can be synchronized into a macroscopic coherent state accompanied by the emission of strong continuous wave THz-radiation. The temperature dependence of the emission is governed by the interplay of self-heating in the resonator and by re-trapping of intrinsic Josephson junctions which can yield a strongly non-monotonic temperature dependence of the emission power. Furthermore, proper shaping of the resonators yields THz-sources with voltage-tunable emission frequencies.
Macroscopic quantum effects in intrinsic Josephson junction stacks
NASA Astrophysics Data System (ADS)
Koyama, T.; Machida, M.
2008-09-01
A macroscopic quantum theory for the capacitively-coupled intrinsic Josephson junctions (IJJ’s) is constructed. We clarify the multi-junction effect for the macroscopic quantum tunneling (MQT) to the first resistive branch. It is shown that the escape rate is greatly enhanced by the capacitive coupling between junctions. We also discuss the origin of the N2-enhancement in the escape rate observed in the uniformly switching in Bi-2212 IJJ’s.
Quantum phases in intrinsic Josephson junctions: Quantum magnetism analogy
NASA Astrophysics Data System (ADS)
Machida, Masahiko; Kobayashi, Keita; Koyama, Tomio
2013-08-01
We explore quantum phases in intrinsic Josephson junction (IJJ) stacks, whose in-plane area is so small that the capacitive coupling has a dominant role in the superconducting phase dynamics. In such cases, the effective Hamiltonian for the superconducting phase can be mapped onto that of one-dimensional ferromagnetically-interacting spin model, whose spin length S depends on the magnitude of the on-site Coulomb repulsion. The ferromagnetic model for IJJ’s prefers synchronized quantum features in contrast to the antiferromagnetically-interacting model in the conventional Josephson junction arrays.
Collective Dynamics of Intrinsic Josephson Junctions in HTSC
NASA Astrophysics Data System (ADS)
Shukrinov, Yu M.; Mahfouzi, F.
2006-06-01
The dynamics of a stack of intrinsic Josephson junctions (IJJ) in the high-Tc superconductors is theoretically investigated with both the quasineutrality breakdown effect and quasiparticle charge imbalance effect taken into account. The current-voltage characteristics (IVC) of IJJ are numerically calculated in the framework of capacitively coupled Josephson junctions model and charge imbalance model including set of differential equations for phase differences, kinetic equations and generalized Josephson relations. We obtain the branch structure in IVC and investigate it as a function of model parameters such as coupling constant, McCumber parameter and number of junctions in the stack. The dependence of branch slopes and branch endpoints on the coupling and disequilibrium parameters are found. We study the nonequilibrium effects created by current injection and show that the increase in the disequilibrium parameter changes essentially the character of IVC. The new features of the hysteresis behavior of IVC of IJJ are obtained.
Small-number arrays of intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Yurgens, A.; Torstensson, M.; You, L. X.; Bauch, T.; Winkler, D.; Kakeya, I.; Kadowaki, K.
2008-04-01
Arrays of nanometre-thick Bi2212-intrinsic Josephson junctions (IJJ's) are studied in various geometries. The samples with only a few IJJ's allow for the intrinsic-tunnelling spectroscopy with minimum of Joule heating. The reproducible low-voltage peaks of the spectra probably stem from a superconducting gap which is half the usual size. We estimate the internal temperature in the IJJ stacks and analyze the importance of the self-heating for the macroscopic-quantum-tunnelling experiments involving IJJ's.
Planar intrinsic Josephson junctions fabricated on Bi-2212 LPE films
NASA Astrophysics Data System (ADS)
Yasuda, Takashi; Kawae, Takeshi; Yamashita, Tsutomu; Taka, Chihiro; Nishida, Akihiko; Takano, Shuzo
2003-05-01
Planar design of intrinsic Josephson junctions (IJJs) is studied using Bi2Sr2CaCu2Ox (Bi-2212) films prepared by liquid phase epitaxy. Step-type IJJ stacks fabricated on step-patterned MgO substrates exhibit multibranched current-voltage characteristics inherent in Bi-2212 single crystals. This behavior is found to be limited to films on small-angle steps, suggesting the incorporation of defects near the steep steps of substrates.
Single intrinsic Josephson junction with double-sided fabrication technique
NASA Astrophysics Data System (ADS)
You, L. X.; Torstensson, M.; Yurgens, A.; Winkler, D.; Lin, C. T.; Liang, B.
2006-05-01
We make stacks of intrinsic Josephson junctions (IJJs) embedded in the bulk of very thin (d⩽100nm) Bi2Sr2CaCu2O8+x single crystals. By precisely controlling the etching depth during the double-sided fabrication process, the stacks can be reproducibly tailor-made to be of any microscopic height (0-9nm
MQT observation in Bi2212 intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Kashiwaya, Satoshi; Matsumoto, Tetsuro; Kashiwaya, Hiromi; Shibata, Hajime; Eisaki, Hiroshi; Yoshida, Yoshiyuki; Kawabata, Shiro; Tanaka, Yukio
2007-09-01
The quantum dynamics of Bi 2Sr 2CaCu 2O 8+ δ intrinsic Josephson junctions (IJJ’s) is studied based on the escape rate measurements. The saturations observed in the escape temperature and the width of the switching current below 0.45 K (= T∗) indicate the transition of the switching mechanism from the thermal activation to the macroscopic quantum tunneling at T∗. It is shown that most of the switching properties are consistently explained in terms of the underdamped Josephson junction with quality factor of about 70 in spite of possible damping due to d-wave superconductivity. The present result gives the upper limit of the dissipation of IJJ’s.
Subgap Structures in High-Tc Intrinsic Josephson Junctions
NASA Astrophysics Data System (ADS)
Müller, Paul
1998-03-01
Due to their extremely short coherence length many high-Tc superconductors form natural superconducting multilayers. Adjacent superconducting layers are weakly coupled by the Josephson effect. As a result single crystals act intrinsically as vertical stacks of hundreds of Josephson junctions. We start by summarizing our present state of knowledge, including recent observations of Cherenkov radiation from moving fluxons (G. Hechtfischer, R. Kleiner, A.V. Ustinov, P. Müller, Phys. Rev. Lett. 79, 1365 (1997), and this conference.), and the direct measurement of the (collective) Josephson plasma frequency. We then report on pronounced structures in the current-voltage characteristics of Bi_2Sr_2CaCu_2O8 single crystals, and of Tl_2Ba_2Ca_2Cu_3O_10 thin films. These structures appear well below the superconducting gap, independent on magnetic field and temperatures up to 0.5 T_c(K. Schlenga, G. Hechtfischer, R. Kleiner, W. Walkenhorst, P. Müller, Phys. Rev. Lett. 76, 4943 (1996).). We explain these features by coupling between c-axis phonons and Josephson oscillations(Ch. Helm, Ch. Preis, F. Forsthofer, J. Keller, K. Schlenga, R. Kleiner, P. Müller, Phys. Rev. Lett. 79, 737 (1997).). C-axis lattice vibrations between adjacent superconducting layers are exited by the rf Josephson currents in the resistive state. Our results correspond well to the frequencies of longitudinal c-axis phonons.
Thermally assisted vortex motion in intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Irie, A.; Oya, G.
2008-02-01
The vortex dynamics in intrinsic Josephson junctions (IJJs) at finite temperatures has been investigated numerically by taking into account the thermal fluctuations. Our simulations based on the perturbed, coupled sine-Gordon model successfully reproduce the experimental results associated with the Josephson-vortex flow resistance (JVFR) at low bias currents. Depending on the junction length, bias current, and temperature, the JVFR oscillation is changed from the period of half flux quantum per junction to the period of one flux quantum per junction. It is shown that the oscillation is essentially due to the field dependence of the critical current. At currents slightly exceeding the critical current the stationary vortex lattice structure becomes unstable and an irregular vortex flow can be induced by thermal fluctuations in different junctions. Our simulation results strongly suggest that the triangular lattice of vorticies in the dynamical state is more stable rather than the rectangular one even in a submicrometer IJJ stack when IJJs are biased at a low current.
Generation and Detection of THz Radiation Using Intrinsic Josephson Junctions
NASA Astrophysics Data System (ADS)
Irie, Akinobu; Oikawa, Dai; Oya, Gin-ichiro
We present the generation and detection of terahertz radiation using intrinsic Josephson junctions (IJJs) in Bi2Sr2CaCu2Oy single crystals. This approach allows us to detect THz radiation from large stacks consisting of a few hundred intrinsic Josephson junctions. The lateral dimensions of the fabricated IJJ oscillator mesa range from 290×50 to 290×90 μm2 and the number of IJJs which constitute the mesas is between 100 and 450, while the small mesa with the lateral dimensions of 5 × 5 μm2 is used as the high sensitive THz detector. The largest emission is always observed when the oscillator is biased at the negative resistance region of the current-voltage characteristics. We find that the emission frequency cor-responds to the second harmonics of the in-phase cavity resonance mode. This is consistent with the emission condition of the case of thick IJJ stacks reported previously.
Terahertz Responses of Intrinsic Josephson Junctions in High T{sub C} Superconductors
Wang, H. B.; Wu, P. H.; Yamashita, T.
2001-09-03
High frequency responses of intrinsic Josephson junctions up to 2.5THz, including the observation of Shapiro steps under various conditions, are reported and discussed in this Letter. The sample was an array of intrinsic Josephson junctions singled out from inside a high T{sub C} superconducting Bi{sub 2}Sr {sub 2}CaCu{sub 2}O{sub 8+x} single crystal, with a bow-tie antenna integrated to it. The number of junctions in the array was controllable, the junctions were homogeneous, the distribution of applied irradiation among the junctions was even, and the junctions could synchronously respond to high frequency irradiation.
Theory of phase dynamics in intrinsic Josephson junctions with multigap superconducting layers
NASA Astrophysics Data System (ADS)
Ota, Y.; Machida, M.; Koyama, T.
2011-11-01
We construct a theory of dynamical behavior in intrinsic Josephson junction stacks with multigap superconducting layers. The theory predicts the existence of two kinds of phase modes, one of which is the Josephson-plasma mode and other of which is the Leggett’s mode. We discuss a cooperative phenomena induced by inter-band Josephson coupling in addition to capacitive and inductive couplings between the superconducting layers.
Wendt, Joel R.; Plut, Thomas A.; Martens, Jon S.
1995-01-01
A novel method for fabricating nanometer geometry electronic devices is described. Such Josephson junctions can be accurately and reproducibly manufactured employing photolithographic and direct write electron beam lithography techniques in combination with aqueous etchants. In particular, a method is described for manufacturing planar Josephson junctions from high temperature superconducting material.
Wendt, J.R.; Plut, T.A.; Martens, J.S.
1995-05-02
A novel method for fabricating nanometer geometry electronic devices is described. Such Josephson junctions can be accurately and reproducibly manufactured employing photolithographic and direct write electron beam lithography techniques in combination with aqueous etchants. In particular, a method is described for manufacturing planar Josephson junctions from high temperature superconducting material. 10 figs.
Macroscopic quantum effects in capacitively- and inductively-coupled intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Koyama, T.; Machida, M.
2009-03-01
A theory for macroscopic quantum tunneling (MQT) in intrinsic Josephson junction stacks is formulated. Both capacitive and inductive couplings between junctions are taken into account. We calculate the escape rate in the switching to the first resistive branch in the quantum regime. It is shown that the enhancement of the escape rate is caused mainly by the capacitive coupling between junctions in IJJ's with small in-plane area of ~ 1μm2.
NASA Astrophysics Data System (ADS)
Koyama, Tomio; Ota, Yukihiro; Machida, Masahiko
2011-06-01
We investigate the resonance effect caused by the Josephson-Leggett (JL) mode in intrinsic Josephson junction stacks (IJJs) formed by a stack of multigap superconducting layers. Such an IJJ system is expected to be realized in a single crystal of highly anisotropic iron-based superconductors with thick blocking layers. It is shown that the JL mode is resonantly excited by the Josephson oscillations in the voltage state with inhomogeneous electric-field distribution along the c axis. The resonance creates a steplike structure with a negative resistance region in the I-V characteristics.
Proximity Effect in BSCCO Intrinsic Josephson Junctions Contacted with a Normal Metal Layer
NASA Astrophysics Data System (ADS)
Suzuki, Minoru; Koizumi, Masayuki; Ohmaki, Masayuki; Kakeya, Itsuhiro; Shukrinov, Yu. M.
Superconductivity proximity effect is numerically evaluated based on McMillan's tunneling proximity model for a sandwich of a normal metal layer on top of the surface superconducting layer of intrinsic Josephson junctions in a Bi2Sr2CaCu2O8+δ (BSCCO) crystal. Due to the very thin thickness of 0.3 nm of the superconducting layer in IJJs, the surface layer is subject to influence of the proximity effect when the top layer is contacted with a normal metal layer. The effect manifests itself as a significant change in the characteristics of the IJJ surface Josephson junction. It is found that when the superconducting layer thickness is smaller than 0.6 nm, the pair potential reduces significantly, leading to an almost complete suppression of the critical Josephson current density for the surface junction. This result can partly explain the experimental results on the IJJ characteristics of a mesa type structure.
In-phase electrodynamics and terahertz wave emission in extended intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Koyama, Tomio; Matsumoto, Hideki; Machida, Masahiko; Kadowaki, Kazuo
2009-03-01
Strong emission of subterahertz electromagnetic (EM) waves has been observed recently in the high Tc superconductor Bi2Sr2CaCu2O8 intrinsic Josephson junctions (IJJ’s). We investigate numerically the dynamics of the EM fields both inside and outside the IJJ’s emitting terahertz EM waves under a constant bias current, using two-dimensional models composed of IJJ’s and the space surrounding them: (1) xy model and (2) xz model. In the xy model we investigate the EM modes excited in the rectangular junctions. In the voltage state the Josephson oscillation generates the oscillating EM field having nodes inside the junctions. The number of nodes depends on the DC voltage appearing in the junctions, and their direction is parallel to the shorter side of the junctions. The EM field shows a complex distribution pattern in the near field region. In the region far from the junctions we have only the expanding EM wave oscillating with the Josephson frequency. In the xz model we study the EM waves emitted in the xz plane from the junctions covered with normal electrodes. It is shown that the power of the emitted EM waves has distribution similar to that in the dipole emission in the system where electrodes of the same size are attached on top and bottom junctions. In the asymmetric system where the lower electrode is larger than the upper one the power distribution of emitted EM wave deviates from that in the dipole emission.
RF impedance of intrinsic Josephson junction in flux-flow state with a periodic pinning potential
NASA Astrophysics Data System (ADS)
Yamada, Y.; Nakajima, K.; Nakajima, K.
2008-09-01
We have investigated the dynamics of Josephson vortices interacting with electromagnetic waves in Bi 2Sr 2CaCu 2O 8+ y intrinsic Josephson junction (IJJ) stacks by means of millimeter wave irradiation and numerical simulations based on coupled sine-Gordon equations while taking into account a sinusoidal form of the periodic pinning potential. The numerical simulation results for the influence of the electromagnetic waves on the flux-flow properties reveal that the periodic pinning potential induces the in-phase motion of Josephson vortices over the junctions. In order to prove from another viewpoint, we investigate RF impedance of IJJ in flux-flow state in this study. A remarkable negative real part region appears at 1st harmonic step, it means that the IJJ in flux-flow state acts as an oscillator at the negative real part region.
An effect of temperature distribution on terahertz phase dynamics in intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Asai, Hidehiro; Kawabata, Shiro
2013-11-01
In this study, we numerically calculate the temperature distribution and the THz phase dynamics in the mesa-structured intrinsic Josephson junctions (IJJs) using the thermal diffusion equation and the Sine-Gordon equation. We observe that the temperature distribution has a broad peak around the center region of the IJJ mesa. Under a high external current, a “hot spot” where the temperature is locally higher than the superconducting critical temperature appears around this region. The transverse Josephson plasma wave is strongly excited by the inhomogeneous temperature distribution in the mesa. This gives rise to intense THz emission.
NASA Astrophysics Data System (ADS)
Wang, Huabing; Wu, Peiheng; Yamashita, Tsutomu
2001-10-01
Using a newly developed double-side fabrication method, an IJJ stack plus a bow-tie antenna and chokes were integrated in a slice 200 nm thick and singled out from inside a bulk Bi2Sr2CaCu2O8+x (BSCCO) single crystal. The junctions in the fabricated stack were very uniform, and the number of junctions involved was rather controllable. In addition to this method, which can be used to fabricate integrated circuits based on intrinsic Josephson junctions in high temperature (Tc) superconductors, also reported will be terahertz responses of IJJs, and the possible applications in quantum voltage standard, spectroscopy, and so on.
Macroscopic quantum tunneling in a stack of capacitively-coupled intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Koyama, Tomio; Machida, Masahiko
2008-04-01
A macroscopic quantum theory for the phase dynamics in capacitively-coupled intrinsic Josephson junctions (IJJ's) is constructed. We quantize the capacitively-coupled IJJ model in terms of the canonical quantization method. The multi-junction effect for the macroscopic quantum tunneling (MQT) to the first resistive branch is clarified. It is shown that the escape rate is greatly enhanced by the capacitive coupling between junctions. We also discuss the origin of the N2 -enhancement in the escape rate observed in the uniformly switching in Bi-2212 IJJ's.
NASA Astrophysics Data System (ADS)
Shukrinov, Yu. M.; Rahmonov, I. R.; Plecenik, A.; Streltsova, O. I.; Zuev, M. I.; Ososkov, G. A.
2016-02-01
The current-voltage (IV) characteristics of the intrinsic Josephson junctions in high temperature superconductors under external electromagnetic radiation are calculated numerically in the parametric resonance region. We discuss a numerical method for calculation of the Shapiro step width on the amplitude of radiation. In order to accelerate computations we used parallelization by task parameter via Simple Linux Utility for Resource Management (SLURM) arrays and tested it in the case of a single junction. An analysis of the junction transitions between rotating and oscillating states in the branching region of IV-characteristics is presented.
Experimental and theoretical investigation on high-Tc superconducting intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Grib, Alexander; Shukrinov, Yury; Schmidl, Frank; Seidel, Paul
2010-11-01
Within the last years many groups have realized and investigated different types of intrinsic Josephson junction (IJJ) arrays out of high-temperature superconducting single crystals or thin films. We tried to improve the synchronization between the junctions by external shunts. Mesa structures as well as microbridges on vicinal cut substrates showed multi-branch behaviour in their IV characteristics and random switching between branches. Theoretical modelling was done investigating phase dynamics and stability numerically as well as analytically. Branch structure in current voltage characteristics of IJJ is studied in the framework of different models, particularly, in capacitevely coupled Josephson junctions (CCJJ) model and CCJJ model with diffusion current. Results of modelling of return current in IV characteristics for stacks with different number of IJJ are presented. We discussed the possible mechanisms of synchronization and the ranges of stability. Conclusions with respect to application of such arrays such as radiation sources were given.
Theory for collective macroscopic tunneling in high- Tc intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Machida, M.; Koyama, T.
2007-10-01
On the basis of the theory for the capacitive coupling in intrinsic Josephson junctions (IJJ's), we theoretically study the macroscopic quantum tunneling in the switching dynamics into the voltage states in IJJ. The effective action obtained by using the path integral formalism reveals that the capacitive coupling splits each of the lowest and higher quantum levels, which are given inside Josephson potential barrier of the single junction derived by dropping off the coupling, into levels composed of the number of junction (N). This level splitting can cause multiple low-frequency Rabi-oscillations and enhance the switching probability compared to the conventional Caldeira-Leggett theory. Furthermore, a possibility as a naturally built-in multi-qubit is discussed.
NASA Astrophysics Data System (ADS)
Koyama, T.; Matsumoto, H.; Ota, Y.; Machida, M.
2013-08-01
Electromagnetic (EM) wave emission from the intrinsic Josephson junction stacks (IJJ’s) covered with a thin dielectric medium is numerically investigated, using the multi-scale simulation method developed in our previous paper. It is shown that the power of emitted EM waves is considerably increased in the IJJ’s with a dielectric cover. The emission from the n = 2 resonance mode is greatly enhanced. The enhancement is caused by the excitation of a solitonic mode.
The electric field effect and electromagnetic wave emission in intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Koyama, T.
2013-04-01
We formulate a theory for the electric field effect in intrinsic Josephson junctions (IJJs). The coupled dynamical equations for the phase differences are derived in the presence of both a bias current and an applied electric field on the basis of the capacitively-coupled IJJ model. It is shown that the current-voltage characteristics of the IJJs sensitively depend on the applied electric field. The dipole emission originating from the electric field effect is also predicted.
Mathematical modeling of intrinsic Josephson junctions with capacitive and inductive couplings
NASA Astrophysics Data System (ADS)
Rahmonov, I. R.; Shukrinov, Yu M.; Zemlyanaya, E. V.; Sarhadov, I.; Andreeva, O.
2012-11-01
We investigate the current voltage characteristics (CVC) of intrinsic Josephson junctions (IJJ) with two types of couplings between junctions: capacitive and inductive. The IJJ model is described by a system of coupled sine-Gordon equations which is solved numerically by the 4th order Runge-Kutta method. The method of numerical simulation and numerical results are presented. The magnetic field distribution is calculated as the function of coordinate and time at different values of the bias current. The influence of model parameters on the CVC is studied. The behavior of the IJJ in dependence on coupling parameters is discussed.
Numerical study for electromagnetic wave emission in thin samples of intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Koyama, T.; Matsumoto, H.; Ohta, Y.; Machida, M.
2011-11-01
Emission of THz electromagnetic waves from thin samples of intrinsic Josephson junctions (IJJ’s) is numerically studied, using the xz-model. We show that the spatial symmetry of the electromagnetic excitations corresponding to the π-cavity mode is different from that of the 2 π-cavity mode in the IJJ’s where the junction parameters such as the Josephson critical current are weakly inhomogeneous. In such IJJ’s the emission in the [0 0 1] direction, which is forbidden in the dipole emission, appears at the π-cavity mode resonance, whereas it is not observed in the 2 π-cavity mode resonance. It is also shown that the strong emission occurs when the transition between branches in the I- V characteristics takes place.
Fabrication of submicron La2-xSrxCuO4 intrinsic Josephson junction stacks
NASA Astrophysics Data System (ADS)
Kubo, Yuimaru; Takahide, Yamaguchi; Tanaka, Takayoshi; Ueda, Shinya; Ishii, Satoshi; Tsuda, Shunsuke; Islam, ATM Nazmul; Tanaka, Isao; Takano, Yoshihiko
2011-02-01
Intrinsic Josephson junction (IJJ) stacks of cuprate superconductors have potential to be implemented as intrinsic phase qubits working at relatively high temperatures. We report success in fabricating submicron La2-xSrxCuO4 (LSCO) IJJ stacks carved out of single crystals. We also show a new fabrication method in which argon ion etching is performed after focused ion beam etching. As a result, we obtained an LSCO IJJ stack in which resistive multibranches appeared. It may be possible to control the number of stacked IJJs with an accuracy of a single IJJ by developing this method.
NASA Astrophysics Data System (ADS)
Antonenko, Daniil S.; Skvortsov, Mikhail A.
2015-12-01
A nondissipative supercurrent state of a Josephson junction is metastable with respect to the formation of a finite-resistance state. This transition is driven by fluctuations, thermal at high temperatures and quantum at low temperatures. We evaluate the lifetime of such a state due to quantum fluctuations in the limit when the supercurrent is approaching the critical current. The decay probability is determined by the instanton action for the superconducting phase difference across the junction. At low temperatures, the dynamics of the phase is massive and is determined by the effective capacitance, which is a sum of the geometric and intrinsic capacitance of the junction. We model the central part of the Josephson junction either by an arbitrary short mesoscopic conductor described by the set of its transmission coefficients, or by a diffusive wire of an arbitrary length. The intrinsic capacitance can generally be estimated as C*˜G /Eg , where G is the normal-state conductance of the junction and Eg is the proximity minigap in its normal part. The obtained capacitance is sufficiently large to qualitatively explain the hysteretic behavior of the current-voltage characteristic even in the absence of overheating.
Solitons in Josephson junctions
NASA Astrophysics Data System (ADS)
Ustinov, A. V.
1998-11-01
Magnetic flux quanta in Josephson junctions, often called fluxons, in many cases behave as solitons. A review of recent experiments and modelling of fluxon dynamics in Josephson circuits is presented. Classic quasi-one-dimensional junctions, stacked junctions (Josephson superlattices), and discrete Josephson transmission lines (JTLs) are discussed. Applications of fluxon devices as high-frequency oscillators and digital circuits are also addressed.
Current-induced in-plane superconducting transition in intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
You, L. X.; Yurgens, A.; Winkler, D.; Torstensson, M.; Kajiki, K.; Tanaka, I.
2006-05-01
In stacks of intrinsic Josephson junctions (IJJs) with lateral sizes of several microns, the current is non-uniform in many cases. In certain geometries a significant part of the current flows along the superconducting planes and can reach the critical value. The current-driven superconductivity breakdown within a single Cu2O4 plane can be seen as an extra branch structure of the c-axis current-voltage characteristics. This allows us to deduce the sheet critical current of a single Cu2O4 plane in different measurement configurations. The conditions for the observation of such a current-induced transition in different IJJ geometries are discussed.
Terahertz wave emission from intrinsic Josephson junctions in high- Tc superconductors
NASA Astrophysics Data System (ADS)
Ozyuzer, L.; Simsek, Y.; Koseoglu, H.; Turkoglu, F.; Kurter, C.; Welp, U.; Koshelev, A. E.; Gray, K. E.; Kwok, W. K.; Yamamoto, T.; Kadowaki, K.; Koval, Y.; Wang, H. B.; Müller, P.
2009-11-01
Recently, we experimentally demonstrated that rectangular mesa structures of intrinsic Josephson junctions (IJJ) in Bi2Sr2CaCu2O8+d (Bi2212) can be used as a compact solid-state generator of continuous, coherent and polarized terahertz (THz) radiation. In the present work, we will exhibit tall mesas (over 600 junctions) which were fabricated using UV lithography, e-beam lithography with photoresist and e-beam lithography with a Ti selective etching technique. We will present measurements of the c-axis resistance as a function of temperature and of current-voltage characteristics of THz emitting mesas with lateral sizes ranging from 30 × 300 to 100 × 300 µm2. Furthermore, we will discuss the dependence of the characteristics of the mesa structures on the oxygen doping level of the Bi2212 crystals. We will also experimentally show that the voltage-frequency relation of the ac Josephson effect has to match the cavity resonance for successful emission.
Terahertz wave emission from intrinsic Josephson junctions in high-T{sub c} superconductors.
Ozyuzer, L.; Simsek, Y.; Koseoglu, H.; Turkoglu, F.; Kurter, C.; Welp, U.; Koshelev, A. E.; Gray, K. E.; Kwok, W. K.; Yamamoto, T.; Kadowaki, K.; Koval, Y.; Wang, H. B.; Muller, P.; Materials Science Division; Izmir Inst. of Tech.; Univ. of Erlangen-Nurnberg; Univ. of Tsukuba; National Inst. for Materials Science
2009-10-20
Recently, we experimentally demonstrated that rectangular mesa structures of intrinsic Josephson junctions (IJJ) in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+d} (Bi2212) can be used as a compact solid-state generator of continuous, coherent and polarized terahertz (THz) radiation. In the present work, we will exhibit tall mesas (over 600 junctions) which were fabricated using UV lithography, e-beam lithography with photoresist and e-beam lithography with a Ti selective etching technique. We will present measurements of the c-axis resistance as a function of temperature and of current-voltage characteristics of THz emitting mesas with lateral sizes ranging from 30 x 300 to 100 x 300 {micro}m{sup 2}. Furthermore, we will discuss the dependence of the characteristics of the mesa structures on the oxygen doping level of the Bi2212 crystals. We will also experimentally show that the voltage-frequency relation of the ac Josephson effect has to match the cavity resonance for successful emission.
Ozyuzer, L.; Ozdemir, M.; Kurter, C.; Hinks, D. G.; Gray, K. E.
2007-01-01
The interlayer tunneling spectroscopy has been performed on micron-sized mesa arrays of HgBr{sub 2} intercalated superconducting Bi2212 single crystals. A ferromagnetic multilayer (Au/Co/Au) is deposited on top of the mesas. The spin-polarized current is driven along the c-axis of the mesas through a ferromagnetic Co layer and the hysteretic quasiparticle branches are observed at 4.2 K. Magnetic field evolution of hysteretic quasiparticle branches is obtained to examine the effect of injected spin-polarized current on intrinsic Josephson junction characteristics. It is observed that there is a gradual distribution in quasiparticle branches with the application of magnetic field and increasing field reduces the switching current progressively.
Vortex Penetrations in Parallel-connected two Stacks of Intrinsic Josephson Junctions
NASA Astrophysics Data System (ADS)
Ooi, Shuuichi; Mochiku, Takashi; Tachiki, Minoru; Hirata, Kazuto
In mesoscopic stacks of intrinsic Josephson junctions (IJJs) in Bi2Sr2CaCu2O8+y (Bi2212), the penetrations of individual vortices are detectable by the measurements of the transport properties, i.e., c-axis resistance or critical current. We have measured the c-axis resistance as a function of magnetic field in samples with two stacks of IJJs connected in parallel by Bi2212 itself to study any interaction of individual vortex penetrations into them. Since the superconducting loop containing two stacks of IJJs is the same geometry as that of superconducting quantum interference device (SQUID), we might expect a periodic resistance (or current) modulation as a function of magnetic field, whose period corresponds to the area in the loop. However, the results were just simple mixing of the resistive changes by the individual vortex penetrations into each of the stacks; behavior like SQUID has not been observed in present samples.
NASA Astrophysics Data System (ADS)
Kashiwagi, T.; Yamamoto, T.; Minami, H.; Tsujimoto, M.; Yoshizaki, R.; Delfanazari, K.; Kitamura, T.; Watanabe, C.; Nakade, K.; Yasui, T.; Asanuma, K.; Saiwai, Y.; Shibano, Y.; Enomoto, T.; Kubo, H.; Sakamoto, K.; Katsuragawa, T.; Marković, B.; Mirković, J.; Klemm, R. A.; Kadowaki, K.
2015-11-01
The intrinsic Josephson junctions (IJJs) in the high-Tc superconductor Bi2Sr2CaCu2O8 +δ (Bi2212) are shown to have great potential for the construction of an oscillator emitting in the terahertz-frequency f regime. However, earlier devices with Bi2212 substrates exhibit strong self-heating effects detrimental to their operation and limiting the maximum f to approximately 1 THz. Here we describe an efficient fabrication procedure for a stand-alone-mesa IJJ terahertz oscillator with considerably reduced self-heating effects, greatly expanding the tunability and maximum value of f , potentially even to 15 THz. Their typical current-voltage characteristics, radiation tunability and power, and some practical uses are also presented.
Tunneling characteristics for nm-thick mesas consisting of a few intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Suzuki, Minoru; Ohmaki, Masayuki; Takemura, Ryota; Hamada, Kenji; Watanabe, Takao; Ota, Kensuke; Kitano, Haruhisa; Maeda, Atsutaka
2008-10-01
Very thin mesa structures consisting of a few intrinsic Josephson junctions have been fabricated on single crystal surfaces of Bi2Sr2CaCu2O8+δ. In the fabrication procedure, annealing is conducted after the mesa structure is formed by Ar ion milling. Or, the annealing is skipped and, instead, the electrodes to the mesas have been deposited in vacuum immediately after crystals are cleaved. We have attained both uniform current-voltage (I-V) characteristics and small contact resistances, which are usually difficult to obtain at the same time in the case of nm-thick mesa structures. For the mesas thus fabricated, it is found that the Josephson critical current Jc of the top IJJ (the surface junction) is reduced significantly. The reduction of Jc is more significant when the doping level of the crystal used is lower. We argue that this is due to the proximity efiect of the surface junction, in which the top electrode is in close proximity with the Ag or Au film of a thickness of the order of 300 nm. For mesas obtained by this method, the switching probability distribution has been measured. It is found that when the mesa lateral size is larger than 2 μm the switching is unreproducible and lacking systematic temperature dependence. It is also found that escape temperature Tesc and the standard deviation σ for the switching probability distribution exhibits a large deviation from the Kramers' thermal activation theory. When the lateral size is no larger than 2 μm, the switching probability distribution results show coincidence with the theory in the temperature range from 1.3 K to 5 K. Below 0.5 K, the escape temperature tends to saturate and indicates a crossover near 0.5 K from the thermal activation to the macroscopic quantum tunneling.
Mutual synchronization of two stacks of intrinsic Josephson junctions in cuprate superconductors
Lin, Shi-Zeng
2014-05-07
Certain high-T{sub c} cuprate superconductors, which naturally realize a stack of Josephson junctions, thus can be used to generate electromagnetic waves in the terahertz region. A plate-like single crystal with 10{sup 4} junctions without cavity resonance was proposed to achieve strong radiation. For this purpose, it is required to synchronize the Josephson plasma oscillation in all junctions. In this work, we propose to use two stacks of junctions shunted in parallel to achieve synchronization. The two stacks are mutually synchronized in the whole IV curve, and there is a phase shift between the plasma oscillation in the two stacks. The phase shift is nonzero when the number of junctions in different stacks is the same, while it can be arbitrary when the number of junctions is different. This phase shift can be tuned continuously by applying a magnetic field when all the junctions are connected by superconducting wires.
NASA Astrophysics Data System (ADS)
Yamada, Y.; Nakajima, K.; Nakajima, K.
2009-10-01
We reported dynamics of Josephson vortices interacting with electromagnetic waves in strongly coupled long Josephson junctions stack, such as an intrinsic Josephson junction (IJJ), by numerical simulations based on coupled sine-Gordon equations considering a periodic pinning potential of sinusoidal form. The numerical simulation results for the influence of the electromagnetic waves on flux-flow properties show that the periodic pinning potential induces an in-phase motion of Josephson vortices over the junction stacks, which achieve high performances of IJJ flux-flow oscillator. In order to prove it from another viewpoint, we calculate RF impedance of long Josephson junction stacks in flux-flow state. A remarkable negative real part region of RF impedance appears at 1st harmonic step, it means that the long Josephson junction stacks in flux-flow state acts as an oscillator at the negative real part region. In this study, we evaluate the optimum condition for RF radiation with the periodic pinning potential.
Characterization of intrinsic Josephson junctions for La 2- xSr xCuO 4 single crystals
NASA Astrophysics Data System (ADS)
Uematsu, Y.; Mizugaki, Y.; Nakajima, K.; Yamashita, T.; Watauchi, S.; Tanaka, I.
2002-02-01
We have fabricated c-axis micro-bridges of La 2- xSr xCuO 4 (LSCO) single crystals in order to characterize the LSCO intrinsic Josephson junctions (IJJs). The current-voltage characteristics of the micro-bridges exhibited a large hysteresis with a voltage jump of the order 0.5-3 V and no multiple branching structures. A superconducting energy gap was clearly observed on the quasi-particle branch and showed BCS-like temperature dependence. In addition, the temperature dependence of the critical current of the IJJ was in good agreement with the theoretical curves for superconductor-insulator-superconductor (SIS) Josephson junctions. These results demonstrate that the IJJs of LSCO are characterized as stacked series SIS junctions.
Ozyuzer, L.; Kurter, C.; Ozdemir, M.; Zasadzinski, J. F.; Gray, K. E.; Hinks, D. G.
2007-06-01
To investigate the effect of polarized current on tunneling characteristics of intrinsic Josephson junctions (IJJs), spin-polarized and spin-degenerate current have been injected through the c-axis of HgBr{sub 2} intercalated Bi{sub 2.1}Sr{sub 1.5}Ca{sub 1.4}Cu{sub 2}O{sub 8+delta} (Bi2212) single crystals on which 10 times 10 mum{sup 2} mesas have been fabricated. These two spin conditions are achieved by depositing either Au (15 nm)/Co (80 nm)/Au (156 nm) multilayers or single Au film on HgBr{sub 2} intercalated Bi2212 with T{sub c} = 74 K followed by photolithography and Ar ion beam etching. The I-V characteristics have been measured with and without a magnetic field parallel to c-axis at 4.2 K. A fine, soft Au wire is used to make a gentle mechanical contact on the top of a particular mesa in the array. Tunneling conductance characteristics were obtained and the magnetic field dependence of sumgap voltage peaks was investigated. These peaks do not change in position with increasing magnetic field for both contact configurations. In addition, the temperature dependence of tunneling characteristics of the IJJs are obtained and existence of pseudogap feature is observed above T{sub c} for HgBr{sub 2} intercalated Bi2212.
Terahertz-wave emission from Bi2212 intrinsic Josephson junctions: a review on recent progress
NASA Astrophysics Data System (ADS)
Kakeya, Itsuhiro; Wang, Huabing
2016-07-01
Emission of terahertz (THz) electromagnetic (EM) waves from a high critical temperature (T c) superconductor intrinsic Josephson junction (IJJ) is a new and promising candidate for practical applications of superconducting devices. From the engineering viewpoint, the IJJ THz source is competitive against the present semiconducting THz sources such as quantum cascade lasers (QCLs) and resonance tunnelling diode oscillators because of its broad tunable frequency range and ease of the fabrication process for the device. The emitted EM waves are considered to be coherent because the emission is yielded by synchronisation of thousand stacked IJJs consisting of the mesa device. This synchronisation is peculiar: the resonant frequency of each IJJ is distributed because the cross section of the mesa device is trapezoidal in shape. One of the key features of the synchronisation mechanism is the temperature inhomogeneity of the emitting device. In this topical review, we describe the recent progress in studies of IJJ THz sources with particular emphasis on the relevance of the temperature inhomogeneity to the synchronisation and the emission intensity. This review is of specific interest because the IJJ THz source shows the rich variety of functions due to self-heating which has always been a detrimental feature in the present superconducting devices. Moreover, the thermal managements used for IJJ THz sources will be common with those of other semiconducting devices such as QCLs. In addition, this review is to invite the readers into related research through the detailed descriptions of experimental procedures.
Enhancement of the critical current of intrinsic Josephson junctions by carrier injection
NASA Astrophysics Data System (ADS)
Kizilaslan, O.; Simsek, Y.; Aksan, M. A.; Koval, Y.; Müller, P.
2015-08-01
We present a study of the doping effect by carrier injection of high-Tc superconducting Bi-based whiskers. The current was injected in the c-axis direction, i.e., perpendicular to the superconducting planes. Superconducting properties were investigated systematically as a function of the doping level. The doping level of one and the same sample was changed by current injection in very small steps from an underdoped state up to a slightly overdoped state. We have observed that Tc versus log (jc) exhibits a dome-shaped characteristic, which can be fitted by a parabola. As Tc versus carrier concentration has a parabolic form, too, it can be concluded that the critical current density jc increases exponentially with the doping level. The electron-trapping mechanism is interpreted in the framework of Phillips’ microscopic theory. In addition, the Joule heating effect in the intrinsic Josephson junction (IJJ) was controlled by carrier injection, and the effect of the non-equilibrium quasiparticle on the I-V curves of the IJJs was also discussed.
Direct observation of intrinsic Josephson junction characteristics in electron-doped Sm2-xCexCuO4-δ
NASA Astrophysics Data System (ADS)
Kawakami, Tsuyoshi; Suzuki, Minoru
2007-10-01
We have investigated the current-voltage (CV) characteristics of the intrinsic Josephson junctions (IJJs) in the electron-doped high- Tc superconductor Sm2-xCexCuO4-δ by using a small mesa structure fabricated on a single crystal surface. It is found that multiple resistive branches, i.e., typical IJJ characteristics, are observed in the CV characteristics when the junction area of a mesa is 10μm2 or less. It is also found that a typical Josephson critical current density Jc is 7.5kA/cm2 at 4.2K for Tc=20.7K . The Josephson penetration depth is experimentally estimated to be 1.0-1.6μm from the size dependence of Jc . Both Jc and Tc are found to decrease with the carrier doping level, as is found for hole-doped Bi2Sr2CaCu2O8+δ in the heavily overdoped region. These results are discussed in relation to the current locking in terms of the coupled Josephson junction stack model.
NASA Technical Reports Server (NTRS)
Thompson, E. D.
1973-01-01
A theory is presented which, though too simple to explain quantitative details in the Josephson junction mixing response, is sufficient for explaining qualitatively the results observed. Crucial to the theory presented, and that which differentiates it from earlier ones, is the inclusion of harmonic voltages across the ideal Josephson element.
NASA Astrophysics Data System (ADS)
Kashiwagi, T.; Nakade, K.; Saiwai, Y.; Minami, H.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y.; Tsujimoto, M.; Yamamoto, T.; Marković, B.; Mirković, J.; Klemm, R. A.; Kadowaki, K.
2014-02-01
A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-Tc superconductor Bi2Sr2CaCu2O8+δ was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.
Resonant phase escape in Bi2Sr2CaCu2O8+δ surface intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Yu, H. F.; Zhu, X. B.; Ren, J. K.; Peng, Z. H.; Cui, D. J.; Deng, H.; Cao, W. H.; Tian, Ye; Chen, G. H.; Zheng, D. N.; Jing, X. N.; Lu, Li; Zhao, S. P.
2013-09-01
We present a study of phase escape in surface Bi2Sr2CaCu2O8+δ intrinsic Josephson junctions in the presence of microwave radiation. The measured switching current distributions display clear double-peak structures in the microwave field, which result from the single- and two-photon resonant escape processes accompanied by microwave-induced potential barrier suppression. We show that these results can be well explained by a quantum-mechanical model proposed by Fistul et al (2003 Phys. Rev. B 68 060504), from which the power and frequency dependences of the switching current distributions can be reproduced.
NASA Astrophysics Data System (ADS)
Kubo, Yuimaru; Sboychakov, A. O.; Nori, Franco; Takahide, Y.; Ueda, S.; Tanaka, I.; Islam, A. T. M. N.; Takano, Y.
2012-10-01
We performed measurements of switching current distribution in a submicrometer La2-xSrxCuO4 (LSCO) intrinsic Josephson junction (IJJ) stack in a wide temperature range. The escape rate saturates below approximately 2 K, indicating that the escape event is dominated by a macroscopic quantum tunneling (MQT) process with a crossover temperature T*≈2K. We applied the theory of MQT for IJJ stacks, taking into account dissipation and the phase retrapping effect in the LSCO IJJ stack. The theory is in good agreement with the experiment both in the MQT and in the thermal activation regimes.
NASA Astrophysics Data System (ADS)
Kitano, Haruhisa; Takahashi, Yusaku; Kakehi, Daiki; Yamaguchi, Hikaru; Koizumi, Shin-ichiro; Ayukawa, Shin-ya
2016-05-01
We report a detailed study of the phase switching rate from the first to the fourth switch for a small stack of Bi2Sr2CaCu2Oy intrinsic Josephson junctions (IJJs). Experimental results were analyzed by using the conventional single-junction model including the thermally-activated phase escape and the multiple phase retrapping. It is shown that the phase retrapping effects are more prominent for higher order switches, even for the underdamped IJJs showing a large hysteresis in the current–voltage characteristics. This clearly suggests that the tilted washboard potential representing the phase switch from the finite voltage state in IJJs can be influenced by a rapid oscillation generated in a phase-switched junction.
Fabrication of Ultrasmall High-Quality Bi2Sr2CaCu2O8+δ Intrinsic Josephson Junctions
NASA Astrophysics Data System (ADS)
Matsumoto, Tetsuro; Kashiwaya, Hiromi; Shibata, Hajime; Eisaki, Hiroshi; Yoshida, Yoshiyuki; Kashiwaya, Satoshi
2008-10-01
The fabrication of ultrasmall high-quality intrinsic Josephson junctions (IJJs) using a cuprate superconductor is critical for the realization of a qubit. We investigated the mechanism of damage induced by a Ga+ beam in a Bi2Sr2CaCu2O8+δ IJJ during focused ion beam (FIB) processing. On the basis of the results, we developed a process that allowed the successful fabrication of an ultrasmall and high-quality IJJ. The damage induced by the FIB is reduced by restricting the direction of the Ga+ beam so that the junction area is not directly irradiated by the ion beam. The fabricated ultrasmall IJJ device has a junction area of 0.3 µm2 and shows excellent current-voltage characteristics.
Intrinsic Josephson junctions in the iron-based multi-band superconductor (V2Sr4O6)Fe2As2
NASA Astrophysics Data System (ADS)
Moll, Philip J. W.; Zhu, Xiyu; Cheng, Peng; Wen, Hai-Hu; Batlogg, Bertram
2014-09-01
In layered superconductors, Josephson junctions may be formed within the unit cell as a result of sufficiently low inter-layer coupling. These intrinsic Josephson junction (iJJ) systems have attracted considerable interest for their application potential in quantum computing as well as efficient sources of THz radiation, closing the famous `THz gap'. So far, iJJ have been demonstrated in single-band, copper-based high-Tc superconductors, mainly in Bi-Sr-Ca-Cu-O (refs , , ). Here we report clear experimental evidence for iJJ behaviour in the iron-based superconductor (V2Sr4O6)Fe2As2. The intrinsic junctions are identified by periodic oscillations of the flux-flow voltage on increasing a well-aligned in-plane magnetic field. The periodicity is explained by commensurability effects between the Josephson vortex lattice and the crystal structure, which is a hallmark signature of Josephson vortices confined into iJJ stacks. This finding adds the pnictide (V2Sr4O6)Fe2As2 to the copper-based iJJ materials of interest for Josephson junction applications. In particular, novel devices based on multi-band Josephson coupling may be realized.
Multi-Junction Switching in Bi2Sr1.6La0.4CuO6+δ Intrinsic Josephson Junctions
NASA Astrophysics Data System (ADS)
Kashiwaya, Hiromi; Matsumoto, Tetsuro; Shibata, Hajime; Eisaki, Hiroshi; Yoshida, Yoshiyuki; Kambara, Hiroshi; Kawabata, Shiro; Kashiwaya, Satoshi
2010-04-01
We study the dynamics of multi-junction switching (MJS): several intrinsic Josephson junctions (IJJs) in an array switch to the finite voltage state simultaneously. The number of multi-switching junctions (N) was successfully tuned by changing the load resistance serially connected to an Bi2Sr1.6La0.4CuO6+δ IJJ array. The independence of the escape rates of N in the macroscopic quantum tunneling regime indicates that MJS is a successive switching process rather than a collective process. The origin of MJS is explained by the gradient of a load curve and the relative magnitudes of the switching currents of quasiparticle branches in the current-voltage plane.
Terahertz electromagnetic radiation from Bi2Sr2CaCu2Oy intrinsic Josephson junction stack
NASA Astrophysics Data System (ADS)
Oikawa, Dai; Irie, Akinobu; Yamaki, Kazuhiro; Oya, Gin-ichiro
We have observed terahertz (THz) electromagnetic wave radiation from Bi2Sr2CaCu2Oy intrinsic Josephson junction (IJJ) stacks using high sensitive detector made of a small IJJ mesa. In this study, we focused on the THz radiation from a few hundred IJJs. We fabricated the IJJ oscillator and detector. The oscillators consist of 55 ∼ 300 IJJs with the lateral dimensions of 290 ¥ 50 μm2. The current-voltage characteristics of the IJJ oscillators showed a negative resistance accompanied with large hysteresis. The THz radiation was observed for several samples when the oscillator was biased at some current in the negative resistance region. We attribute the observed radiation to synchronized emission from many IJJs in the stack and find the emission frequency corresponds to the in-phase cavity resonance frequency.
NASA Astrophysics Data System (ADS)
Nomura, Yoshiki; Mizuno, Takaaki; Kambara, Hitoshi; Nakagawa, Yuya; Kakeya, Itsuhiro
2015-01-01
Macroscopic quantum tunneling (MQT) in an intrinsic Josephson junction (IJJ) stack of Bi1.9Pb0.1Sr1.39La0.63CuO6+δ (BiPb2201) has been investigated. For the first switch, from superconducting to the first resistive branch in current-voltage characteristics, the crossover between MQT and thermal activation (TA) takes place at 0.6 K. On the other hand, for the second switch, the MQT-TA crossover temperature is increased to 2.0 K. This result is interpreted as follows: the MQT rate of the second switch is enhanced by the charge coupling between adjacent IJJs as well as in Bi2Sr2CaCu2O8+δ. We consider that the enhancement of the MQT rate is a common feature among bismuth-cuprates with single and double CuO2 layers in their crystal structures.
Signatures of topological Josephson junctions
NASA Astrophysics Data System (ADS)
Peng, Yang; Pientka, Falko; Berg, Erez; Oreg, Yuval; von Oppen, Felix
2016-08-01
Quasiparticle poisoning and diabatic transitions may significantly narrow the window for the experimental observation of the 4 π -periodic dc Josephson effect predicted for topological Josephson junctions. Here, we show that switching-current measurements provide accessible and robust signatures for topological superconductivity which persist in the presence of quasiparticle poisoning processes. Such measurements provide access to the phase-dependent subgap spectrum and Josephson currents of the topological junction when incorporating it into an asymmetric SQUID together with a conventional Josephson junction with large critical current. We also argue that pump-probe experiments with multiple current pulses can be used to measure the quasiparticle poisoning rates of the topological junction. The proposed signatures are particularly robust, even in the presence of Zeeman fields and spin-orbit coupling, when focusing on short Josephson junctions. Finally, we also consider microwave excitations of short topological Josephson junctions which may complement switching-current measurements.
Enhanced macroscopic quantum tunneling in Bi2Sr2CaCu2O8 + delta intrinsic Josephson-junction stacks.
Jin, X Y; Lisenfeld, J; Koval, Y; Lukashenko, A; Ustinov, A V; Müller, P
2006-05-01
We have investigated macroscopic quantum tunneling in Bi(2)Sr(2)CaCu(2)O(8 + delta) intrinsic Josephson junctions at millikelvin temperatures using microwave irradiation. Measurements show that the escape rate for uniformly switching stacks of Nu junctions is about Nu(2) times higher than that of a single junction having the same plasma frequency. We argue that this gigantic enhancement of the macroscopic quantum tunneling rate in stacks is boosted by current fluctuations which occur in the series array of junctions loaded by the impedance of the environment. PMID:16712327
Josephson junction simulation of neurons
NASA Astrophysics Data System (ADS)
Crotty, Patrick; Schult, Dan; Segall, Ken
2010-07-01
With the goal of understanding the intricate behavior and dynamics of collections of neurons, we present superconducting circuits containing Josephson junctions that model biologically realistic neurons. These “Josephson junction neurons” reproduce many characteristic behaviors of biological neurons such as action potentials, refractory periods, and firing thresholds. They can be coupled together in ways that mimic electrical and chemical synapses. Using existing fabrication technologies, large interconnected networks of Josephson junction neurons would operate fully in parallel. They would be orders of magnitude faster than both traditional computer simulations and biological neural networks. Josephson junction neurons provide a new tool for exploring long-term large-scale dynamics for networks of neurons.
Intrinsic Josephson Junctions in the iron-based multi-band superconductor (V2Sr4O6)Fe2As2
NASA Astrophysics Data System (ADS)
Moll, Philip; Zhu, Xiyu; Cheng, Peng; Wen, Hai-Hu; Bertram, Batlogg
2014-03-01
We have observed clear experimental evidence for intrinsic Josephson junction (iJJ) behavior in the iron-based superconductor (V2Sr4O6)Fe2As2 (Tc ~ 20 K). The iJJs are identified by periodic oscillations of the flux flow voltage for out-of-plane (c-axis) currents upon increasing a well aligned in-plane magnetic field. Their periodicity is well explained by commensurability effects between the Josephson vortex lattice and the crystal structure, which is a hallmark signature of Josephson vortices confined into iJJ stacks. Essential for reliable c-axis transport measurements on the available microcrystals are Focused Ion Beam microstructuring and contacting techniques. The insulating temperature behavior of ρc indicates S-I-S type junctions. This finding adds (V2Sr4O6)Fe2As2 as the first iron-based, multi-band superconductor to the copper-based iJJ materials of interest for Josephson junction applications, and in particular novel devices based on multi-band Josephson coupling may be realized.
Disordered graphene Josephson junctions
NASA Astrophysics Data System (ADS)
Muñoz, W. A.; Covaci, L.; Peeters, F. M.
2015-02-01
A tight-binding approach based on the Chebyshev-Bogoliubov-de Gennes method is used to describe disordered single-layer graphene Josephson junctions. Scattering by vacancies, ripples, or charged impurities is included. We compute the Josephson current and investigate the nature of multiple Andreev reflections, which induce bound states appearing as peaks in the density of states for energies below the superconducting gap. In the presence of single-atom vacancies, we observe a strong suppression of the supercurrent, which is a consequence of strong intervalley scattering. Although lattice deformations should not induce intervalley scattering, we find that the supercurrent is still suppressed, which is due to the presence of pseudomagnetic barriers. For charged impurities, we consider two cases depending on whether the average doping is zero, i.e., existence of electron-hole puddles, or finite. In both cases, short-range impurities strongly affect the supercurrent, similar to the vacancies scenario.
Terahertz emission from a stack of intrinsic Josephson junctions in Bi2Sr2Ca2Cu3O10+δ
NASA Astrophysics Data System (ADS)
Tsujimoto, Manabu; Kakeya, Itsuhiro; Adachi, Shintaro; Watanabe, Takao; Kashiwagi, Takanari; Minami, Hidetoshi; Kadowaki, Kazuo
Terahertz radiation in the 0.3-10 THz frequency range is a technologically attractive form of electromagnetic radiation, because it has applications in numerous fields. Terahertz generation from stacks of intrinsic Josephson junctions fabricated from Bi2Sr2CaCu2O8+δ (Bi-2212) has become a major focus of both experimental and theoretical research [U. Welp et al., Nat. Photonics 7, 702 (2013)]. Here, we observe continuous terahertz emission from a stack of intrinsic Josephson junctions made of Bi2Sr2Ca2Cu3O10+δ (Bi-2223). We investigate how triple CuO2 planes affect the c-axis current-voltage and emission characteristics. The terahertz emission spectra are measured by Fourier-transform infrared spectroscopy.
NASA Astrophysics Data System (ADS)
Kitano, H.; Ota, K.; Hamada, K.; Takemura, R.; Ohmaki, M.; Maeda, A.; Suzuki, M.
2009-03-01
A nanometer-thick small mesa consiting of only two or three Bi2Sr2CaCu2Oy intrinsic Josephson junctions (IJJs) is studied through the switching current distribution measurements down to 0.4 K. Experimental results clearly show that the first switching events from the zero-voltage state for 1 K < T < 4 K are successfully described by a conventional thermal activation (TA) theory for a single Josephson junction, and that they become independent of temperature below T* ~ 0.7 K. We observe the microwave-induced peak in the switching distribution at 0.4 K, which is induced by the microwave irradiation at 55 GHz. These results strongly suggest that the system crossovers to macroscopic quantum tunneling (MQT) regime below T*, which is as high as the previously reported value for a stacked IJJs with several tens of junctions, in contrast to the recent result on a similar mesa-structured surface IJJ.
Wireless Josephson Junction Arrays
NASA Astrophysics Data System (ADS)
Adams, Laura
2015-03-01
We report low temperature, microwave transmission measurements on a wireless two- dimensional network of Josephson junction arrays composed of superconductor-insulator -superconductor tunnel junctions. Unlike their biased counterparts, by removing all electrical contacts to the arrays and superfluous microwave components and interconnects in the transmission line, we observe new collective behavior in the transmission spectra. In particular we will show emergent behavior that systematically responds to changes in microwave power at fixed temperature. Likewise we will show the dynamic and collective response of the arrays while tuning the temperature at fixed microwave power. We discuss these spectra in terms of the Berezinskii-Kosterlitz-Thouless phase transition and Shapiro steps. We gratefully acknowledge the support Prof. Steven Anlage at the University of Maryland and Prof. Allen Goldman at the University of Minnesota. Physics and School of Engineering and Applied Sciences.
NASA Astrophysics Data System (ADS)
Tsujimoto, Manabu; Yamaki, Kazuhiro; Yamamoto, Takashi; Minami, Hidetoshi; Kashiwagi, Takanari; Kadowaki, Kazuo; Tachiki, Masashi
2010-03-01
Intense and coherent terahertz (THz) radiation was observed from the intrinsic Josephson junction (IJJ) system of the single crystalline high-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi-2212).footnotetextL. Ozyuzer et al., Science 318, (2007) 1291.^,footnotetextK. Kadowaki et al., Physica C 468, (2008) 634. In the present work, we demonstrate the importance of the THz radiation from inner branching structures of the I-V characteristic curve of the IJJ system. The radiation frequency has previously been thought to be uniquely constrained to the mesa size, but it turns out in the inner branches that it varies very flexibly and widely perhaps according to the inductive and capacitive coupling strength existing in the mesa itself. Therefore, the radiation frequency does not follow the previously established cavity resonance condition. This new experimental feature may provide a unique opportunity to understand the dynamical nature of IJJ as well as the mechanism of high-Tc superconductivity in this particular Bi-2212 compound.
Li, Shao-Xiong; Qiu, Wei; Han, Siyuan; Wei, Y F; Zhu, X B; Gu, C Z; Zhao, S P; Wang, H B
2007-07-20
We report on the first unambiguous observation of macroscopic quantum tunneling (MQT) in a single submicron Bi(2)Sr(2)CaCu(2)O(8+delta) surface intrinsic Josephson junction (IJJ) by measuring its temperature-dependent switching current distribution. All relevant junction parameters were determined in situ in the classical regime and were used to predict the behavior of the IJJ in the quantum regime via MQT theory. Experimental results agree quantitatively with the theoretical predictions, thus confirming the MQT picture. Furthermore, the data also indicate that the surface IJJ, where the current flows along the c axis of the crystal, has the conventional sinphi current-phase relationship. PMID:17678315
NASA Astrophysics Data System (ADS)
Li, Shao-Xiong; Qiu, Wei; Han, Siyuan; Wei, Y. F.; Zhu, X. B.; Gu, C. Z.; Zhao, S. P.; Wang, H. B.
2007-07-01
We report on the first unambiguous observation of macroscopic quantum tunneling (MQT) in a single submicron Bi2Sr2CaCu2O8+δ surface intrinsic Josephson junction (IJJ) by measuring its temperature-dependent switching current distribution. All relevant junction parameters were determined in situ in the classical regime and were used to predict the behavior of the IJJ in the quantum regime via MQT theory. Experimental results agree quantitatively with the theoretical predictions, thus confirming the MQT picture. Furthermore, the data also indicate that the surface IJJ, where the current flows along the c axis of the crystal, has the conventional sinφ current-phase relationship.
NASA Astrophysics Data System (ADS)
Zhu, Xiao-Bo; Wei, Yan-Feng; Zhao, Shi-Ping; Chen, Geng-Hua; Yang, Qian-Sheng
2004-04-01
Well-characterized surface intrinsic Josephson junctions (IJJs) on Bi2Sr2CaCu2O8+delta single crystals are fabricated by in situ cryogenic cleavage of the crystals and immediate evaporation of Au films on the crystal surface. Magnetic field dependences of the critical currents of the surface and inner IJJs are carefully measured. We find that the critical current behaviour of the surface IJJs in magnetic field is quite different from that of the inner junctions. The behaviour of the inner IJJs can be understood to be of large stacked junctions described by the coupled sine-Gordon equations, while the surface IJJs behave like a separate single large junction. These results indicate that the coupling between the surface IJJ and the inner IJJs is weaker than the coupling among the inner junctions.
NASA Astrophysics Data System (ADS)
Li, Mengyue; Yuan, Jie; Kinev, Nickolay; Li, Jun; Gross, Boris; Guénon, Stefan; Ishii, Akira; Hirata, Kazuto; Hatano, Takeshi; Koelle, Dieter; Kleiner, Reinhold; Koshelets, Valery P.; Wang, Huabing; Wu, Peiheng
2012-08-01
We report on measurements of the linewidth Δf of terahertz radiation emitted from intrinsic Josephson junction stacks, using a Nb/AlN/NbN integrated receiver for detection. Previous resolution-limited measurements indicated that Δf may be below 1 GHz—much smaller than expected from a purely cavity-induced synchronization. While at low bias we found Δf to be not smaller than ˜500 MHz, at high bias, where a hot spot coexists with regions which are still superconducting, Δf turned out to be as narrow as 23 MHz. We attribute this to the hot spot acting as a synchronizing element. Δf decreases with increasing bath temperature, a behavior reminiscent of motional narrowing in NMR or electron spin resonance (ESR), but hard to explain in standard electrodynamic models of Josephson junctions.
Fabrication of submicron La{sub 2-x}Sr{sub x}CuO{sub 4} intrinsic Josephson junction stacks
Kubo, Yuimaru; Takano, Yoshihiko; Takahide, Yamaguchi; Ueda, Shinya; Ishii, Satoshi; Tsuda, Shunsuke; Tanaka, Takayoshi; Islam, ATM Nazmul; Tanaka, Isao
2011-02-01
Intrinsic Josephson junction (IJJ) stacks of cuprate superconductors have potential to be implemented as intrinsic phase qubits working at relatively high temperatures. We report success in fabricating submicron La{sub 2-x}Sr{sub x}CuO{sub 4} (LSCO) IJJ stacks carved out of single crystals. We also show a new fabrication method in which argon ion etching is performed after focused ion beam etching. As a result, we obtained an LSCO IJJ stack in which resistive multibranches appeared. It may be possible to control the number of stacked IJJs with an accuracy of a single IJJ by developing this method.
Confocal Annular Josephson Tunnel Junctions
NASA Astrophysics Data System (ADS)
Monaco, Roberto
2016-04-01
The physics of Josephson tunnel junctions drastically depends on their geometrical configurations and here we show that also tiny geometrical details play a determinant role. More specifically, we develop the theory of short and long annular Josephson tunnel junctions delimited by two confocal ellipses. The behavior of a circular annular Josephson tunnel junction is then seen to be simply a special case of the above result. For junctions having a normalized perimeter less than one, the threshold curves in the presence of an in-plane magnetic field of arbitrary orientations are derived and computed even in the case with trapped Josephson vortices. For longer junctions, a numerical analysis is carried out after the derivation of the appropriate motion equation for the Josephson phase. We found that the system is modeled by a modified and perturbed sine-Gordon equation with a space-dependent effective Josephson penetration length inversely proportional to the local junction width. Both the fluxon statics and dynamics are deeply affected by the non-uniform annulus width. Static zero-field multiple-fluxon solutions exist even in the presence of a large bias current. The tangential velocity of a traveling fluxon is not determined by the balance between the driving and drag forces due to the dissipative losses. Furthermore, the fluxon motion is characterized by a strong radial inward acceleration which causes electromagnetic radiation concentrated at the ellipse equatorial points.
Confocal Annular Josephson Tunnel Junctions
NASA Astrophysics Data System (ADS)
Monaco, Roberto
2016-09-01
The physics of Josephson tunnel junctions drastically depends on their geometrical configurations and here we show that also tiny geometrical details play a determinant role. More specifically, we develop the theory of short and long annular Josephson tunnel junctions delimited by two confocal ellipses. The behavior of a circular annular Josephson tunnel junction is then seen to be simply a special case of the above result. For junctions having a normalized perimeter less than one, the threshold curves in the presence of an in-plane magnetic field of arbitrary orientations are derived and computed even in the case with trapped Josephson vortices. For longer junctions, a numerical analysis is carried out after the derivation of the appropriate motion equation for the Josephson phase. We found that the system is modeled by a modified and perturbed sine-Gordon equation with a space-dependent effective Josephson penetration length inversely proportional to the local junction width. Both the fluxon statics and dynamics are deeply affected by the non-uniform annulus width. Static zero-field multiple-fluxon solutions exist even in the presence of a large bias current. The tangential velocity of a traveling fluxon is not determined by the balance between the driving and drag forces due to the dissipative losses. Furthermore, the fluxon motion is characterized by a strong radial inward acceleration which causes electromagnetic radiation concentrated at the ellipse equatorial points.
Clarke, John; Hilbert, Claude; Hahn, Erwin L.; Sleator, Tycho
1988-01-01
An automatic Q-spoiler comprising at least one Josephson tunnel junction connected in an LC circuit for flow of resonant current therethrough. When in use in a system for detecting the magnetic resonance of a gyromagnetic particle system, a high energy pulse of high frequency energy irradiating the particle system will cause the critical current through the Josephson tunnel junctions to be exceeded, causing the tunnel junctions to act as resistors and thereby damp the ringing of the high-Q detection circuit after the pulse. When the current has damped to below the critical current, the Josephson tunnel junctions revert to their zero-resistance state, restoring the Q of the detection circuit and enabling the low energy magnetic resonance signals to be detected.
Clarke, J.; Hilbert, C.; Hahn, E.L.; Sleator, T.
1986-03-25
An automatic Q-spoiler comprising at least one Josephson tunnel junction connected in an LC circuit for flow of resonant current therethrough. When in use in a system for detecting the magnetic resonance of a gyromagnetic particle system, a high energy pulse of high frequency energy irradiating the particle system will cause the critical current through the Josephson tunnel junctions to be exceeded, causing the tunnel junctions to act as resistors and thereby damp the ringing of the high-Q detection circuit after the pulse. When the current has damped to below the critical current, the Josephson tunnel junctions revert to their zero-resistance state, restoring the Q of the detection circuit and enabling the low energy magnetic resonance signals to be detected.
Simple Electronic Analog of a Josephson Junction.
ERIC Educational Resources Information Center
Henry, R. W.; And Others
1981-01-01
Demonstrates that an electronic Josephson junction analog constructed from three integrated circuits plus an external reference oscillator can exhibit many of the circuit phenomena of a real Josephson junction. Includes computer and other applications of the analog. (Author/SK)
NASA Astrophysics Data System (ADS)
Takahashi, Yusaku; Kakehi, Daiki; Takekoshi, Shuho; Ishikawa, Kazuki; Ayukawa, Shin-ya; Kitano, Haruhisa
2016-07-01
We report a study of the phase escape in Bi2Sr2CaCu2Oy intrinsic Josephson junctions under the strong microwave irradiation, focusing on the switch from the first resistive state (2nd SW). The resonant double-peak structure is clearly observed in the switching current distributions below 10 K and is successfully explained by a quantum-mechanical model on the quantum phase escape under the strong microwave field. These results provide the first evidence for the formation of the energy level quantization for the 2nd SW, supporting that the macroscopic quantum tunneling for the 2nd SW survives up to ˜10 K.
Kashiwagi, T. Minami, H.; Kadowaki, K.; Nakade, K.; Saiwai, Y.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y.; Tsujimoto, M.; Yamamoto, T.; Marković, B.; Mirković, J.; Klemm, R. A.
2014-02-24
A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-T{sub c} superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.
NASA Astrophysics Data System (ADS)
Kakeya, Itsuhiro; Hirayama, Nobuo; Nakagawa, Takuto; Omukai, Yuta; Suzuki, Minoru
2013-08-01
We report on emission of electromagnetic wave in a frequency range of 1012 hertz (THz) from stacks of intrinsic Josephson junctions (IJJ) made of superconducting Bi2Sr2CaCu2O8+δ single crystals. A home-built high-resolution Fourier-transfer-infrared spectrometer reveals that the emission spectrum is monochromatic and the width is as sharp as its resolution limit (∼1 GHz). The THz emission is obtained in a broad temperature and current range depending on the mesa. The emission frequency is tuned from 0.55 to 0.45 THz by changing temperature from 20 to 55 K.
NASA Astrophysics Data System (ADS)
Tsujimoto, Manabu; Nakayama, Ryo; Orita, Naoki; Koike, Takashi; Deguchi, Kota; Delfanazari, Kaveh; Yamamoto, Takashi; Kashiwagi, Takanari; Minami, Hidetoshi; Tachiki, Masashi; Kadowaki, Kazuo
2011-03-01
Intense and coherent terahertz electromagnetic wave (THz-wave) emission from the intrinsic Josephson junctions (IJJs) in single crystalline high-Tc superconductor Bi 2 Sr 2 CaCu 2 O8 + δ (Bi-2212) was reported in 2007 [L. Ozyuzer et al., Science 318, (2007) 1291.]. In the present work, we demonstrate the relationship between the bias condition and the resonance state by controlling both the applied voltage, V , and the number of resistive junctions, N . We directly observed that if N junctions are in resistive state, the resonance frequency, fJ , varies in accordance with the ac-Josephson relation; fJ = (2 | e | / h) V / N , although frequency fJ has previously been thought to be uniquely determined by the geometrical condition due to the cavity resonance effect [M. Tsujimoto et al., Phys. Rev. Lett. 105, (2010) 037005.]. We also found that the emission intensity varies as a function of both fJ and N . CREST-JST, WPI-MANA, Strategic Initiative A (University of Tsukuba).
NASA Astrophysics Data System (ADS)
Sakai, Shigeki; Zhao, Xia
2007-02-01
Flux-flow cavity resonances in intrinsic Josephson junctions (IJJs) with long c-axis periodicity by artificial critical-current (Jc) modulation are studied numerically and theoretically. For an n-1-n-1-n-1-n IJJ system with n-layer high-Jc and one-layer low-Jc alternately stacked, numerical simulation confirms fluxon penetration only in the low-Jc junctions under proper low magnetic fields. The simulation also shows pronounced cavity-resonance steps in the I-V curves of the low-Jc junctions, meaning that fluxon dynamics can be generated under much lower magnetic fields, compared to the fields for usual IJJs with homogeneous Jc. A theoretical method for describing the flux-flow cavity-resonance properties is presented. The general disperse k-ω relationship shows that, at low-k regions, the critical-current-modulated junction system can be regarded as simple homogeneous stacked junctions with a new effective thickness and a new inductive coupling strength. For general-k cases, the cavity-resonant voltage steps on the I-V curves at various magnetic fields can be well indexed by integers, which means excellent agreement between the theoretical analysis and the numerical simulations.
Electrodynamics and intrinsic Josephson effects in multi-gap superconductors
NASA Astrophysics Data System (ADS)
Koyama, Tomio; Ota, Yukihiro; Machida, Masahiko
2010-11-01
We develop a theory for the Josephson effects in 2-gap intrinsic Josephson junction stacks (IJJ's). The coupled dynamical equations for the phase differences are derived from the low-energy effective Lagrangian. The equations can describe the longitudinal Josephson plasma and the Josephson-Leggett (JL) mode propagating in the direction perpendicular to the junctions. Numerical results for the I - V characteristics are presented. The I - V characteristics shows multiple-branch structure similar to that in Bi-2212 IJJ's. When the Josephson frequency is approached to the JL mode frequency in non-uniform voltage branches, the JL mode is resonantly excited. At the resonant voltage a step-like structure appears in the I - V curves in low-voltage branches.
Josephson Effect in SFNS Josephson Junctions
NASA Astrophysics Data System (ADS)
Karminskaya, T. Yu.; Kupriyanov, M. Yu.; Golubov, A. A.; Sidorenko, A. S.
The critical current, I C, of Josephson junctions both in ramp-type (S-FN-S) and in overlap (SNF-FN-FNS, SN-FN-NS, SNF-N-FNS) geometries has been calculated in the frame of linearized Usadel equations (S-superconductor, F-ferromagnetic, N-normal metal). For the ramp-type structures, in which S electrodes contact directly the end walls of FN bilayer, it is shown that I C may exhibit damping oscillations as a function of both the distance L between superconductors and thicknesses d F,N of ferromagnetic and normal layers. The conditions have been determined under which the decay length and period of oscillation of I C(L) at fixed d F are of the order of decay length of superconducting correlations in the N metal, ξN, that is much larger than in F film. In overlap configurations, in which S films are placed on the top of NF bilayer, the studied junctions have complex SNF or SN electrodes (N or NF bilayer are situated under a superconductor). We demonstrate that in these geometries the critical current can exceed that in ramp-type junctions. Based on these results, the choice of the most practically applicable geometry is discussed.
Josephson junctions and dark energy
NASA Astrophysics Data System (ADS)
Jetzer, Philippe; Straumann, Norbert
2006-08-01
In a recent paper Beck and Mackey [C. Beck, M.C. Mackey, astro-ph/0603397] argue that the argument we gave in our paper [Ph. Jetzer, N. Straumann, Phys. Lett. B 606 (2005) 77, astro-ph/0411034] to disprove their claim that dark energy can be discovered in the Lab through noise measurements of Josephson junctions is incorrect. In particular, they emphasize that the measured noise spectrum in Josephson junctions is a consequence of the fluctuation dissipation theorem, while our argument was based on equilibrium statistical mechanics. In this note we show that the fluctuation dissipation relation does not depend upon any shift of vacuum (zero-point) energies, and therefore, as already concluded in our previous paper, dark energy has nothing to do with the proposed measurements.
NASA Astrophysics Data System (ADS)
Yurgens, A.; Bulaevskii, L. N.
2011-01-01
We numerically study Joule heating in a THz emitter made of Bi2Sr2CaCu2O8 + δ (Bi2212) single crystal with its CuO planes oriented perpendicular to supporting substrate. The single crystal is glued to the substrate by a layer of PMMA. The electrical current is applied in the c-axis direction across many intrinsic Josephson junctions (IJJ's) in Bi2212. The calculations show that the internal temperature increases to an acceptable 10-20 K only above the bath temperature for a Joule power density of ~ 105 W cm - 3 typical for experiments on THz emission from IJJ's. This makes the suggested geometry promising for boosting the output power of the emitter.
NASA Astrophysics Data System (ADS)
Ota, K.; Hamada, K.; Takemura, R.; Ohmaki, M.; Machi, T.; Tanabe, K.; Suzuki, M.; Maeda, A.; Kitano, H.
2009-04-01
We investigated macroscopic quantum tunneling (MQT) of Bi2Sr2CaCu2Oy intrinsic Josephson junctions (IJJs) for two device structures. One is a small mesa, which is a few nanometers thick with only two or three IJJs, and the other is a stack of a few hundred IJJs in a narrow bridge structure. The experimental results regarding the switching-current distribution for the first switch from the zero-voltage state were in good agreement with the conventional theory for a single Josephson junction, indicating that the crossover temperature from thermal activation to the MQT regime for the former device structure was similar to that for the latter device structure. Together with the observation of multiphoton transitions between quantized energy levels in the MQT regime, these results strongly suggest that the observed MQT behavior is intrinsic to a single IJJ in high- Tc cuprates and is independent of the device structure. The switching-current distribution for the second switch from the first resistive state, which was carefully distinguished from the first switch, was also compared with respect to the two device structures. In spite of the differences between the heat transfer environments, the second switch exhibited a similar temperature-independent behavior for both devices up to a much higher temperature than the crossover temperature for the first switch. We argue that this cannot be explained in terms of self-heating caused by dissipative currents after the first switch. As possible candidates for this phenomenon, the MQT process for the second switch and the effective increase in the electronic temperature due to the quasiparticle injection are discussed.
New lock-in phenomena in intrinsic Josephson junctions of Bi2Sr2CaCu2O8+y with hole-array
NASA Astrophysics Data System (ADS)
Hirata, K.; Ooi, S.; Mochiku, T.
2013-08-01
Dynamical behaviour of Josephson and pancake vortices (JVs and PVs) in intrinsic Josephson junctions of Bi2Sr2CaCu2O8+y (Bi-2212) single crystal with a nano-size hole-array has been studied to measure the flow-resistance of the vortices. In the magnetic field perpendicular to the superconducting layers, flow resistance of PVs measured with the in-plane current shows a matching behaviour as usually observed at the matching fields. After the measurements, the sample was fabricated into the in-line shaped structure for the c-axis current measurements to obtain the JV flow-resistance. Instead of the usually-observed lock-in phenomenon of JVs in Bi-2212, several peaks are observed with changing the angle from the in-plane magnetic field to show the enhancement of the flow-resistance at some typical angles. When PVs are introduced into the sample with changing the angle, are trapped into holes, and are interacted with JVs, it is clearly seen that the well-aligned PVs cause the enhancement of the JV flow-resistance.
NASA Astrophysics Data System (ADS)
Oya, G.; Miyasaka, T.; Kitamura, M.; Irie, A.
We have studied the response of stacks of intrinsic Josephson junctions (IJJs) of (Bi1-xPbx)2Sr2CaCu2Oy (x = 0.15) to injection of microwave of frequencies frf of 2-20 GHz at 4.2 K and higher temperatures. Clear constant voltage steps, which are considered Shapiro steps, are successfully observed on the current-voltage characteristic of an IJJ with a resistivity of Josephson-vortex flow Rfl in any stack under the injection of microwave. The step of the eighth order, which is the highest in this study, is observed from the largest IJJ under injection of microwave of 10 GHz at 4.2 K. But, as the temperature increases, the number of steps decreases, and finally the steps disappear at ∼45 K due to large self-heating. In this IJJ a low Rfl plays an important role in appearance of the steps of the high order. The typical behavior of the steps at 4.2 K is well reproduced by numerical simulations on that of Shapiro steps of a JJ with the shunt resistivity equal to Rfl at the temperature.
NASA Astrophysics Data System (ADS)
Rudau, F.; Wieland, R.; Langer, J.; Zhou, X. J.; Ji, M.; Kinev, N.; Hao, L. Y.; Huang, Y.; Li, J.; Wu, P. H.; Hatano, T.; Koshelets, V. P.; Wang, H. B.; Koelle, D.; Kleiner, R.
2016-04-01
We use 2D coupled sine-Gordon equations combined with 3D heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a 250 ×70 μ m2 intrinsic Josephson junction stack. The 700 junctions are grouped to 20 segments; we assume that in a segment all junctions behave identically. At large input power, a hot spot forms in the stack. Resonant electromagnetic modes oscillating either along the length [(0, n ) modes] or the width [(m , 0) modes] of the stack or having a more complex structure can be excited both with and without a hot spot. At fixed bath temperature and bias current, several cavity modes can coexist in the absence of a magnetic field. The (1, 0) mode considered to be the most favorable mode for terahertz emission can be stabilized by applying a small magnetic field along the length of the stack. A strong field-induced enhancement of the emission power is also found in experiment for an applied field around 5.9 mT.
NASA Astrophysics Data System (ADS)
Cui, D. J.; Yu, H. F.; Peng, Z. H.; Cao, W. H.; Zhu, X. B.; Tian, Ye; Chen, G. H.; Lin, D. H.; Gu, C. Z.; Zheng, D. N.; Jing, X. N.; Lu, Li; Zhao, S. P.
2008-12-01
Macroscopic quantum tunneling (MQT) has been demonstrated recently in a Bi2Sr2CaCu2O8+δ surface intrinsic Josephson junction (SIJJ) with its critical current density Jc below 100 A cm-2 and its size below 1 µm. In this work, we present a study of the switching current distributions of SIJJs fabricated on the same crystal, with Jc>500 A cm-2 and size of 0.8 and 1.6 µm. MQT is clearly observed, and the crossover from MQT to thermal activation (TA) is seen. Our analysis shows that the data agree well with the theoretical predictions of MQT and TA for different-sized SIJJs when parameters that roughly scale with the SIJJ size are used. In the crossover regime, the data are found to be better fitted by considering quantum corrections to TA. We discuss the realistic design of phase- and flux-type qubits using the experimentally attainable SIJJ parameters, which shows that the SIJJs, with their controllable Jc and size (or junction capacitance), are feasible for qubit applications in the future.
NASA Astrophysics Data System (ADS)
Kitamura, Michihide; Irie, Akinobu; Oya, Gin-Ichiro
2007-08-01
Conditions to observe Shapiro steps clearly and stably are studied for an intrinsic Josephson junction (IJJ) in Bi2Sr2CaCu2O8+δ high- Tc superconductors. The current equation normalized by the critical current Ic(T) is solved fully numerically. In the calculations, the quasiparticle tunneling current is evaluated by using the normalized I-V characteristics obtained within the d -wave symmetry superconducting gap, while the Cooper-pair (CP) one is calculated on the basis of the general way in which the coherent and incoherent CP tunneling currents can be correctly calculated within the d -wave treatment and the current due to thermal noises is also simulated by using normal random numbers. It is found that the product SRshunt of the junction cross section S and the shunt resistance Rshunt , and the critical current density Jc are important junction parameters, and moreover, that the current equation of the IJJ with no shunt resistance depends on only a universal curve μ(i0) as a function of the normalized external dc current i0 . Furthermore, the effects of the noise, the normalized CP tunneling currents, the SRshunt product, the normalized amplitude ir of external ac modulation, and the Jc on observing the Shapiro steps are studied. When the IJJ is operated under the condition that the shunt resistance is added and the external ac modulation frequency fr is higher than the plasma frequency fp , it is found that (1) clear and stable Shapiro steps with good responses are obtained within the wide range of ir , (2) the response does not so largely depend on the value of SRshunt , and (3) the response for the high Jc junction is much better than that for the low one.
NASA Astrophysics Data System (ADS)
Kadowaki, Kazuo
2013-03-01
After the discovery of intense, coherent and continuous electromagnetic waves at terahertz frequencies (THz waves) in 2007,[2] a number of experimental and theoretical works have been carried out to understand the THz radiation phenomena from mesa structure of layered high temperature superconductor Bi2Sr2CaCu2O8+δ (hereafter abbreviated as Bi2212). At present after five year intensive studies, the basic mechanism of the THz wave emission can be understood by two principles: one is the ac-Josephson effect working in-between individual intrinsic Josephson junctions in the mesa of Bi2212 and the other is the cavity resonance effect associated with both the geometrical shape and the electromagnetic properties of the mesa structures of Bi2212. However, the precise conditions to obtain strong THz radiation are not yet established well at the stage of mesa fabrication.[3] Moreover, it appears that our recent results of measurement of the inhomogeneous temperature distribution due to the hot-spot formation producing gigantic Joule heat in the mesa may give us much more complicated situations to understand physics of the THz radiation.[4] In this talk based on the experimental results we will provide a unified picture of the THz radiation phenomena in spite of highly nonequilibrium thermal condition, which hopefully will give us a hint to improve the performance and the efficiency of the emission power exceeding 1 mW from a single mesa structure. This will be also useful for various applications. This work was supported in part by CREST project at JST and WPI MANA project at NIMS.
Intrinsic Josephson effect and single Cooper pair tunneling
NASA Astrophysics Data System (ADS)
Yamashita, Tsutomu; Kim, Sang-Jae; Latyshev, Yuri; Nakajima, Kensuke
2000-06-01
We proposed a new, small and fast switching gate based on the intrinsic Josephson effect of single crystals of a cuprate superconductor. The switching time is of subpicosecond order, and the operating frequency is up to several terahertz. We used the focused-ion-beam (FIB) method for the fabrication of small Bi 2Sr 2CaCu 2O 8 (Bi-2212) stacked intrinsic Josephson junctions (IJJ) with in-plane size down to the submicron level without the degradation of their Tc. We observed clear Fraunhofer patterns in Ic- B curves and flux-flow velocity of up to 10 6 m/s for the stack junctions with the size of several micrometer scale. For the submicron junction, the low-temperature behavior is governed by the Coulomb-charging effects. This is the first observation of the Coulomb-charging effects in layered high- Tc materials.
New Phenomena in Josephson SINIS Junctions
NASA Astrophysics Data System (ADS)
Volkov, A. F.
1995-06-01
We analyze the dc and ac Josephson effects in SaINISb junctions in which an additional bias current flows in the N layer. The case of low temperatures and voltages \\(eV, T<<Δ\\) is considered in the dirty limit. We show that the critical Josephson current may change sign, and the considered SINIS junction may become a π junction if the voltage drop across the N/Sa interface exceeds a certain value \\(eVN>Δ/2\\). The ac Josephson effect may arise even if the current flows only through the N/Sa interface, whereas the current through the Sb/N interface is absent.
Quantum dynamics in the bosonic Josephson junction
Chuchem, Maya; Cohen, Doron; Smith-Mannschott, Katrina; Hiller, Moritz; Kottos, Tsampikos; Vardi, Amichay
2010-11-15
We employ a semiclassical picture to study dynamics in a bosonic Josephson junction with various initial conditions. Phase diffusion of coherent preparations in the Josephson regime is shown to depend on the initial relative phase between the two condensates. For initially incoherent condensates, we find a universal value for the buildup of coherence in the Josephson regime. In addition, we contrast two seemingly similar on-separatrix coherent preparations, finding striking differences in their convergence to classicality as the number of particles increases.
NASA Astrophysics Data System (ADS)
Liu, X.; Wang, P.; Xie, W.; Ma, L. J.; Zhao, X. J.; He, M.; Ji, L.; Zhang, X.
2015-12-01
An intrinsic Josephson junctions (IJJs) microbridge with planar equiangular spiral antenna (PESA) is proposed and studied by simulation and experiment. This IJJs circuit is simulated firstly to obtain the minimum of reflection coefficient and pattern. Secondly, IJJs with PESA are fabricated on misaligned Tl2Ba2CaCu2O8 superconducting film. The millimeter wave characteristics are investigated by a Febry-Pérot resonator, which consists of a spherical mirror antenna and a plane mirror. At 37.4 GHz, the IJJs and the millimeter wave show an optimum coupling, which deviate from the simulation for only 0.004 GHz. In addition, the extent of the coupling between IJJs and the resonator is discussed at different angle for the polarization direction of the spherical mirror antenna with the microbridge. The result shows that the strongest coupling is obtained at 0-30° angle. Good conformance of measurements and simulations illustrate the effectiveness of our design in strong coupling between sample and resonator.
Hot Spot and THz Wave Generation in Bi2Sr2CaCu2O8 Intrinsic Josephson Junction Stacks
NASA Astrophysics Data System (ADS)
Kleiner, Reinhold
2013-03-01
Stacks of intrinsic Josephson junctions made of the high temperature superconductor Bi2Sr2CaCu2O8 have been shown to emit coherent radiation at THz frequencies. Emission is observed both in a low bias regime and a high bias regime. While at low bias the temperature of the stack is close to the bath temperature, at high bias a hot spot and a standing wave, formed in the ``cold'' part of the stack, coexist. THz radiation is very stable in this regime, exhibiting a linewidth which is much smaller than expected from a purely cavity-induced synchronization mechanism. We investigate the interaction of hot spots and THz waves using a combination of transport measurement, direct electromagnetic wave detection and low temperature scanning laser microscopy (LTSLM). In this talk recent developments will be presented, with a focus on the mechanism of hot spot formation. In collaboration with B. Gross, S. Guénon, M. Y. Li, J. Yuan, N. Kinev, J. Li, A. Ishii, K. Hirata, T. Hatano, R. G. Mints, D. Koelle, V. P. Koshelets, H. B. Wang and P. H. Wu.
NASA Astrophysics Data System (ADS)
Fujino, H.; Kume, E.; Sugimata, E.; Zhao, X.; Sakai, S.
2004-10-01
Integrated test chips of Bi 2Sr 2CaCu 2O x thin-film-type intrinsic Josephson junctions (IJJs) are fabricated, and the yield of showing proper IJJ characteristics is examined. The thin-film type is expected to be suitable for applications to integrated circuits using THz electromagnetic waves, but its low fabrication yield is an issue to be solved. The chip size is 12 × 12 mm 2 in which 90 IJJs are included. Bi 2Sr 2CaCu 2O x thin films are prepared via two steps. First the films are deposited on a low temperature (200 °C) substrate by a precisely controlled evaporation method. Next they are annealed at high temperatures (875 and 878 °C). The annealing time is varied to find an optimum condition. The best chip has a 70% yield of showing multiple-branch structure that is the most typical current vs voltage characteristics of IJJs. The relationship between the yield and the surface smoothness and the IJJ size dependence of the yield are also discussed.
NASA Astrophysics Data System (ADS)
Yuan, J.; Li, M. Y.; Li, J.; Gross, B.; Ishii, A.; Yamaura, K.; Hatano, T.; Hirata, K.; Takayama-Muromachi, E.; Wu, P. H.; Koelle, D.; Kleiner, R.; Wang, H. B.
2012-07-01
Terahertz (THz) emission has been recently detected from intrinsic Josephson junction (IJJ) stacks made of the high critical temperature superconductor Bi2Sr2CaCu2O8+δ (BSCCO). The most employed structure is a mesa standing on a big pedestal of a single crystal with a thin gold layer as its top electrode. In this work, a large (300 × 50 × 1.2 μm3) IJJ stack with superconducting electrodes was fabricated and studied. The stack consisted of N ≈ 800 IJJs. It was prepared with a double-sided fabrication process, and significant THz emission was detected. The output power is comparable to the emission power detected from mesa structures, obviously not weakened by the superconducting upper electrode. The observation of THz emission from the double-sided structure suggests that off-chip THz emission from IJJs can be obtained not only from mesa structures and, most importantly, that the emission power can be potentially enhanced in integrated multi-stack radiation sources.
Spectroscopy Measurements of Magnesium Diboride Josephson Junctions
NASA Astrophysics Data System (ADS)
Mlack, J. T.; Lambert, J. G.; Carabello, S. A.; Thrailkill, Z. E.; Galwaduge, P. T.; Ramos, R. C.
2010-03-01
MgB2 has the highest Tc of the conventional superconductors at 39K and exhibits two superconducting energy bands. This material is also inexpensive to produce and has been utilized in new designs for MRI, RF cavities, and Josephson junctions. We report results of recent spectroscopy and transport measurements of Josephson junctions made of MgB2 obtained from our collaborators. We investigate its transport characteristics at sub-kelvin temperatures as well as its responses to resonant microwave activation.
Quantum Coherence in a Superfluid Josephson Junction
Narayana, Supradeep; Sato, Yuki
2011-02-04
We report a new kind of experiment in which we take an array of nanoscale apertures that form a superfluid {sup 4}He Josephson junction and apply quantum phase gradients directly along the array. We observe collective coherent behaviors from aperture elements, leading to quantum interference. Connections to superconducting and Bose-Einstein condensate Josephson junctions as well as phase coherence among the superfluid aperture array are discussed.
Advanced Concepts in Josephson Junction Reflection Amplifiers
NASA Astrophysics Data System (ADS)
Lähteenmäki, Pasi; Vesterinen, Visa; Hassel, Juha; Paraoanu, G. S.; Seppä, Heikki; Hakonen, Pertti
2014-06-01
Low-noise amplification at microwave frequencies has become increasingly important for the research related to superconducting qubits and nanoelectromechanical systems. The fundamental limit of added noise by a phase-preserving amplifier is the standard quantum limit, often expressed as noise temperature . Towards the goal of the quantum limit, we have developed an amplifier based on intrinsic negative resistance of a selectively damped Josephson junction. Here we present measurement results on previously proposed wide-band microwave amplification and discuss the challenges for improvements on the existing designs. We have also studied flux-pumped metamaterial-based parametric amplifiers, whose operating frequency can be widely tuned by external DC-flux, and demonstrate operation at pumping, in contrast to the typical metamaterial amplifiers pumped via signal lines at.
Instability of Driven Josephson Vortices in Long Underdamped Junctions
NASA Astrophysics Data System (ADS)
Sheikhzada, Ahmad; Gurevich, Alex
We show that a Josephson vortex driven by a dc current can become unstable due to strong Cherenkov radiation resulting from intrinsic nonlocal electrodynamics of long underdamped Josephson junctions. This instability is not captured by the conventional sine-Gordon equation but is described by a more general integro-differential equation for the phase difference, θ (x , t) . Our numerical simulations of this nonlinear dynamic equation for different junction geometries have shown that, as the vortex reaches a critical velocity, it triggers a cascade of expanding vortex-antivortex pairs. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. Our results suggest that a rapidly moving Josephson vortex can destroy the superconducting long-range order in a way that is similar to the crack propagation in solids. This work was supported by DOE under Grant No. DE-SC0010081.
Phonon Josephson junction with nanomechanical resonators
NASA Astrophysics Data System (ADS)
Barzanjeh, Shabir; Vitali, David
2016-03-01
We study coherent phonon oscillations and tunneling between two coupled nonlinear nanomechanical resonators. We show that the coupling between two nanomechanical resonators creates an effective phonon Josephson junction, which exhibits two different dynamical behaviors: Josephson oscillation (phonon-Rabi oscillation) and macroscopic self-trapping (phonon blockade). Self-trapping originates from mechanical nonlinearities, meaning that when the nonlinearity exceeds its critical value, the energy exchange between the two resonators is suppressed, and phonon Josephson oscillations between them are completely blocked. An effective classical Hamiltonian for the phonon Josephson junction is derived and its mean-field dynamics is studied in phase space. Finally, we study the phonon-phonon coherence quantified by the mean fringe visibility, and show that the interaction between the two resonators may lead to the loss of coherence in the phononic junction.
Ultimately short ballistic vertical graphene Josephson junctions
Lee, Gil-Ho; Kim, Sol; Jhi, Seung-Hoon; Lee, Hu-Jong
2015-01-01
Much efforts have been made for the realization of hybrid Josephson junctions incorporating various materials for the fundamental studies of exotic physical phenomena as well as the applications to superconducting quantum devices. Nonetheless, the efforts have been hindered by the diffusive nature of the conducting channels and interfaces. To overcome the obstacles, we vertically sandwiched a cleaved graphene monoatomic layer as the normal-conducting spacer between superconducting electrodes. The atomically thin single-crystalline graphene layer serves as an ultimately short conducting channel, with highly transparent interfaces with superconductors. In particular, we show the strong Josephson coupling reaching the theoretical limit, the convex-shaped temperature dependence of the Josephson critical current and the exceptionally skewed phase dependence of the Josephson current; all demonstrate the bona fide short and ballistic Josephson nature. This vertical stacking scheme for extremely thin transparent spacers would open a new pathway for exploring the exotic coherence phenomena occurring on an atomic scale. PMID:25635386
PHONONS IN INTRINSIC JOSEPHSON SYSTEMS
C. PREIS; K. SCHMALZL; ET AL
2000-10-01
Subgap structures in the I-V curves of layered superconductors are explained by the excitation of phonons by Josephson oscillations. In the presence of a magnetic field applied parallel to the layers additional structures due to fluxon motion appear. Their coupling with phonons is investigated theoretically and a shift of the phonon resonances in strong magnetic fields is predicted.
NASA Astrophysics Data System (ADS)
Kakeya, I.; Fukui, K.; Kawamata, K.; Yamamoto, T.; Kadowaki, K.
2008-04-01
The c-axis resistance in Bi2Sr2CaCu2O8+δ intrinsic Josephson junctions (IJJs) with areas of the ab-plane less than 2 μm2 were measured as functions of applied magnetic field and angle to the crystalline axes. When the magnetic field is tilted off from the lock-in state of Josephson vortices, several sharp dips are found. The separation between the dips approaches to the value corresponding to ϕ0 with further tilting the external magnetic field. This behavior is attributed to the penetration of a quantized pancake vortex into the tiny IJJ. This argument is further supported by the result that the c-axis resistance under magnetic fields parallel to the c-axis shows identical stepwise behavior.
Josephson junctions with alternating critical current density
Mints, R.G.; Kogan, V.G.
1997-04-01
The magnetic-field dependence of the critical current I{sub c}(H) is considered for a short Josephson junction with the critical current density j{sub c} alternating along the tunnel contact. Two model cases, periodic and randomly alternating j{sub c}, are treated in detail. Recent experimental data on I{sub c}(H) for grain-boundary Josephson junctions in YBa{sub 2}Cu{sub 3}O{sub x} are discussed. {copyright} {ital 1997} {ital The American Physical Society}
Supercurrent in van der Waals Josephson junction.
Yabuki, Naoto; Moriya, Rai; Arai, Miho; Sata, Yohta; Morikawa, Sei; Masubuchi, Satoru; Machida, Tomoki
2016-01-01
Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a non-superconducting material between two superconductors to decouple their wavefunctions. These Josephson junctions have been employed in fields ranging from digital to quantum electronics, yet their functionality is limited by the interface quality and use of non-superconducting material. Here we show that by exfoliating a layered dichalcogenide (NbSe2) superconductor, the van der Waals (vdW) contact between the cleaved surfaces can instead be used to construct a Josephson junction. This is made possible by recent advances in vdW heterostructure technology, with an atomically flat vdW interface free of oxidation and inter-diffusion achieved by eliminating all heat treatment during junction preparation. Here we demonstrate that this artificially created vdW interface provides sufficient decoupling of the wavefunctions of the two NbSe2 crystals, with the vdW Josephson junction exhibiting a high supercurrent transparency. PMID:26830754
Axion mass estimates from resonant Josephson junctions
NASA Astrophysics Data System (ADS)
Beck, Christian
2015-03-01
Recently it has been proposed that dark matter axions from the galactic halo can produce a small Shapiro step-like signal in Josephson junctions whose Josephson frequency resonates with the axion mass (Beck, 2013). Here we show that the axion field equations in a voltage-driven Josephson junction environment allow for a nontrivial solution where the axion-induced electrical current manifests itself as an oscillating supercurrent. The linear change of phase associated with this nontrivial solution implies the formal existence of a large magnetic field in a tiny surface area of the weak link region of the junction which makes incoming axions decay into microwave photons. We derive a condition for the design of Josephson junction experiments so that they can act as optimum axion detectors. Four independent recent experiments are discussed in this context. The observed Shapiro step anomalies of all four experiments consistently point towards an axion mass of (110±2) μeV. This mass value is compatible with the recent BICEP2 results and implies that Peccei-Quinn symmetry breaking was taking place after inflation.
Supercurrent in van der Waals Josephson junction
Yabuki, Naoto; Moriya, Rai; Arai, Miho; Sata, Yohta; Morikawa, Sei; Masubuchi, Satoru; Machida, Tomoki
2016-01-01
Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a non-superconducting material between two superconductors to decouple their wavefunctions. These Josephson junctions have been employed in fields ranging from digital to quantum electronics, yet their functionality is limited by the interface quality and use of non-superconducting material. Here we show that by exfoliating a layered dichalcogenide (NbSe2) superconductor, the van der Waals (vdW) contact between the cleaved surfaces can instead be used to construct a Josephson junction. This is made possible by recent advances in vdW heterostructure technology, with an atomically flat vdW interface free of oxidation and inter-diffusion achieved by eliminating all heat treatment during junction preparation. Here we demonstrate that this artificially created vdW interface provides sufficient decoupling of the wavefunctions of the two NbSe2 crystals, with the vdW Josephson junction exhibiting a high supercurrent transparency. PMID:26830754
Supercurrent in van der Waals Josephson junction
NASA Astrophysics Data System (ADS)
Yabuki, Naoto; Moriya, Rai; Arai, Miho; Sata, Yohta; Morikawa, Sei; Masubuchi, Satoru; Machida, Tomoki
2016-02-01
Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a non-superconducting material between two superconductors to decouple their wavefunctions. These Josephson junctions have been employed in fields ranging from digital to quantum electronics, yet their functionality is limited by the interface quality and use of non-superconducting material. Here we show that by exfoliating a layered dichalcogenide (NbSe2) superconductor, the van der Waals (vdW) contact between the cleaved surfaces can instead be used to construct a Josephson junction. This is made possible by recent advances in vdW heterostructure technology, with an atomically flat vdW interface free of oxidation and inter-diffusion achieved by eliminating all heat treatment during junction preparation. Here we demonstrate that this artificially created vdW interface provides sufficient decoupling of the wavefunctions of the two NbSe2 crystals, with the vdW Josephson junction exhibiting a high supercurrent transparency.
Kurter, C.; Ozyuzer, L.; Zasadzinski, J. F.; Hinks, D. G.; Gray, K. E.
2010-11-01
The c-axis current-voltage I(V) characteristics have been obtained on a set of mesas of varying height sculpted on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi2212) crystals intercalated with HgB{sub 2}. The intercalation, along with the small number of junctions in the mesa, N = 6-30, minimizes the degree of self-heating, leading to a consistent Josephson critical current, I{sub C}, among junctions in the mesa. The Bi2212 crystals with a bulk T{sub C} = 74 K are overdoped and display negligible pseudogap effects allowing an accurate measure of the normal state resistance, R{sub N}. These properties make the mesas nearly ideal for the determination of the Josephson I{sub C}R{sub N} product. We find I{sub C}R{sub N} values consistently {approx}30% of the quasiparticle gap parameter, {Delta}/e, which was measured independently using a mechanical contact, break junction technique. The latter was necessitated by higher bias heating effects in the mesas which prevented direct measurements of the superconducting gap. These values are among the highest reported and may represent the maximum intrinsic value for I{sub C}R{sub N}. The results indicate that the c-axis transport is a mixture of coherent and incoherent tunneling.
Measurements of the 1/f Noise in Josephson Junctions for Potential Use as QUbits
NASA Astrophysics Data System (ADS)
Mugford, Chas; Kycia, Jan; Korn, Matthias; Mueck, Michael; Clarke, John
2004-03-01
Critical current fluctuations can be a major source of intrinsic decoherence of qubits based on Josephson junctions. We have measured the 1/f noise due to critical current fluctuations in macroscopic ( area ≈ 2 × 2 μ m^2 ) Josephson junctions. We directly measure changes δ Ic in the critical current Ic of a voltage biased junction and find the magnitude of the critical current fluctuations to be δ I_c/Ic ≈ 10-5 at a frequency of 1 Hz.^ A second way in which we determine 1/f flux noise due to critical current fluctuations is by measuring the flux noise of either dc or rf SQUIDs. In order to not exceed the critical current of the Josephson junction, we operate the rf SQUID in the dispersive mode. By using the same device as dc or rf SQUID, we can compare the 1/f noise of voltage biased and non-voltage biased Josephson junctions.
Holographic Josephson junction from massive gravity
NASA Astrophysics Data System (ADS)
Hu, Ya-Peng; Li, Huai-Fan; Zeng, Hua-Bi; Zhang, Hai-Qing
2016-05-01
We study the holographic superconductor-normal metal-superconductor (SNS) Josephson junction in de Rham-Gabadadze-Tolley massive gravity. If the boundary theory is independent of spatial directions, i.e., if the chemical potential is homogeneous in spatial directions, we find that the graviton mass parameter will make it more difficult for the normal metal-superconductor phase transition to take place. In the holographic model of the Josephson junction, it is found that the maximal tunneling current will decrease according to the graviton mass parameter. Besides, the coherence length of the junction decreases as well with respect to the graviton mass parameter. If one interprets the graviton mass parameter as the effect of momentum dissipation in the boundary field theory, this indicates that the stronger the momentum dissipation is, the smaller the coherence length is.
Strain-tunable Josephson current in graphene-superconductor junction
NASA Astrophysics Data System (ADS)
Wang, Y.; Liu, Y.; Wang, B.
2013-10-01
Strain effects on Josephson current in a graphene-superconductor junction are explored theoretically. It is demonstrated that the supercurrent is an oscillatory function of zigzag direction strain with a strain-dependent oscillating frequency. Interestingly, it is found that the Josephson current under armchair direction strain can be turned on/off with a cutoff strain. In view of the on/off properties of the Josephson current, we propose the strained graphene Josephson junction to be utilized as a supercurrent switch.
Radiation comb generation with extended Josephson junctions
Solinas, P.; Bosisio, R.; Giazotto, F.
2015-09-21
We propose the implementation of a Josephson radiation comb generator based on an extended Josephson junction subject to a time dependent magnetic field. The junction critical current shows known diffraction patterns and determines the position of the critical nodes when it vanishes. When the magnetic flux passes through one of such critical nodes, the superconducting phase must undergo a π-jump to minimize the Josephson energy. Correspondingly, a voltage pulse is generated at the extremes of the junction. Under periodic driving, this allows us to produce a comb-like voltage pulses sequence. In the frequency domain, it is possible to generate up to hundreds of harmonics of the fundamental driving frequency, thus mimicking the frequency comb used in optics and metrology. We discuss several implementations through a rectangular, cylindrical, and annular junction geometries, allowing us to generate different radiation spectra and to produce an output power up to 10 pW at 50 GHz for a driving frequency of 100 MHz.
Overdamped Josephson junctions for digital applications
NASA Astrophysics Data System (ADS)
Febvre, P.; De Leo, N.; Fretto, M.; Sosso, A.; Belogolovskii, M.; Collot, R.; Lacquaniti, V.
2013-01-01
An interesting feature of Superconductor-Normal metal-Superconductor Josephson junctions for digital applications is due to their non-hysteretic current-voltage characteristics in a broad temperature range below Tc. This allows to design Single-Flux-Quantum (SFQ) cells without the need of external shunts. Two advantages can be drawn from this property: first the SFQ cells can be more compact which leads to a more integrated solution towards nano-devices and more complex circuits; second the absence of electrical parasitic elements associated with the wiring of resistors external to the Josephson junctions increases the performance of SFQ circuits, in particular regarding the ultimate speed of operation. For this purpose Superconductor-Normal metal-Insulator-Superconductor Nb/Al-AlOx/Nb Josephson junctions have been recently developed at INRiM with aluminum layer thicknesses between 30 and 100 nm. They exhibit non-hysteretic current-voltage characteristics with IcRn values higher than 0.5 mV in a broad temperature range and optimal Stewart McCumber parameters at 4.2 K for RSFQ applications. The main features of obtained SNIS junctions regarding digital applications are presented.
Fractional Solitons in Excitonic Josephson Junctions.
Hsu, Ya-Fen; Su, Jung-Jung
2015-01-01
The Josephson effect is especially appealing to physicists because it reveals macroscopically the quantum order and phase. In excitonic bilayers the effect is even subtler due to the counterflow of supercurrent as well as the tunneling between layers (interlayer tunneling). Here we study, in a quantum Hall bilayer, the excitonic Josephson junction: a conjunct of two exciton condensates with a relative phase ϕ0 applied. The system is mapped into a pseudospin ferromagnet then described numerically by the Landau-Lifshitz-Gilbert equation. In the presence of interlayer tunneling, we identify a family of fractional sine-Gordon solitons which resemble the static fractional Josephson vortices in the extended superconducting Josephson junctions. Each fractional soliton carries a topological charge Q that is not necessarily a half/full integer but can vary continuously. The calculated current-phase relation (CPR) shows that solitons with Q = ϕ0/2π is the lowest energy state starting from zero ϕ0 - until ϕ0 > π - then the alternative group of solitons with Q = ϕ0/2π - 1 takes place and switches the polarity of CPR. PMID:26511770
Fractional Solitons in Excitonic Josephson Junctions
Hsu, Ya-Fen; Su, Jung-Jung
2015-01-01
The Josephson effect is especially appealing to physicists because it reveals macroscopically the quantum order and phase. In excitonic bilayers the effect is even subtler due to the counterflow of supercurrent as well as the tunneling between layers (interlayer tunneling). Here we study, in a quantum Hall bilayer, the excitonic Josephson junction: a conjunct of two exciton condensates with a relative phase ϕ0 applied. The system is mapped into a pseudospin ferromagnet then described numerically by the Landau-Lifshitz-Gilbert equation. In the presence of interlayer tunneling, we identify a family of fractional sine-Gordon solitons which resemble the static fractional Josephson vortices in the extended superconducting Josephson junctions. Each fractional soliton carries a topological charge Q that is not necessarily a half/full integer but can vary continuously. The calculated current-phase relation (CPR) shows that solitons with Q = ϕ0/2π is the lowest energy state starting from zero ϕ0 – until ϕ0 > π – then the alternative group of solitons with Q = ϕ0/2π − 1 takes place and switches the polarity of CPR. PMID:26511770
Fractional Solitons in Excitonic Josephson Junctions
NASA Astrophysics Data System (ADS)
Hsu, Ya-Fen; Su, Jung-Jung
2015-10-01
The Josephson effect is especially appealing to physicists because it reveals macroscopically the quantum order and phase. In excitonic bilayers the effect is even subtler due to the counterflow of supercurrent as well as the tunneling between layers (interlayer tunneling). Here we study, in a quantum Hall bilayer, the excitonic Josephson junction: a conjunct of two exciton condensates with a relative phase ϕ0 applied. The system is mapped into a pseudospin ferromagnet then described numerically by the Landau-Lifshitz-Gilbert equation. In the presence of interlayer tunneling, we identify a family of fractional sine-Gordon solitons which resemble the static fractional Josephson vortices in the extended superconducting Josephson junctions. Each fractional soliton carries a topological charge Q that is not necessarily a half/full integer but can vary continuously. The calculated current-phase relation (CPR) shows that solitons with Q = ϕ0/2π is the lowest energy state starting from zero ϕ0 - until ϕ0 > π - then the alternative group of solitons with Q = ϕ0/2π - 1 takes place and switches the polarity of CPR.
Boson Josephson Junction with Trapped Atoms
NASA Astrophysics Data System (ADS)
Raghavan, S.; Smerzi, A.; Fantoni, S.; Shenoy, S. R.
We consider coherent atomic tunneling between two weakly coupled Bose-Einstein condensates at T=0 in a double-well trap. The condensate dynamics of the macroscopic amplitudes in the two wells is modeled by two Gross-Pitaevskii equations (GPE) coupled by a tunneling matrix element. Analytic elliptic function solutions are obtained for the time evolution of the inter-well fractional population imbalance z(t) (related to the condensate phase difference) of the Boson Josephson junction (BJJ). Surprisingly, the neutral-atom BJJ shows (non-sinusoidal generalizations of) effects seen in charged-electron superconductor Josephson junctions (SJJ). The BJJ elliptic-function behavior has a singular dependence on a GPE parameter ratio Λ at a critical ratio Λ=Λc, beyond which a novel 'macroscopic quantum self-trapping' effect sets in with a non-zero time-averaged imbalance
Josephson Junctions Help Measure Resonance And Dispersion
NASA Technical Reports Server (NTRS)
Javadi, Hamid H. S.; Mcgrath, William R.; Bumble, Bruce; Leduc, Henry G.
1994-01-01
Electrical characteristics of superconducting microstrip transmission lines measured at millimeter and submillimeter wavelengths. Submicron Josephson (super-conductor/insulator/superconductor) junctions used as both voltage-controlled oscillators and detectors to measure frequencies (in range of hundreds of gigahertz) of high-order resonant electromagnetic modes of superconducting microstrip transmission-line resonators. This oscillator/detector approach similar to vacuum-tube grid dip meters and transistor dip meters used to probe resonances at much lower frequencies.
Very large thermophase in ferromagnetic Josephson junctions.
Giazotto, F; Heikkilä, T T; Bergeret, F S
2015-02-13
The concept of thermophase refers to the appearance of a phase gradient inside a superconductor originating from the presence of an applied temperature bias across it. The resulting supercurrent flow may, in suitable conditions, fully counterbalance the temperature-bias-induced quasiparticle current therefore preventing the formation of any voltage drop, i.e., a thermovoltage, across the superconductor. Yet, the appearance of a thermophase is expected to occur in Josephson-coupled superconductors as well. Here, we theoretically investigate the thermoelectric response of a thermally biased Josephson junction based on a ferromagnetic insulator. In particular, we predict the occurrence of a very large thermophase that can reach π/2 across the contact for suitable temperatures and structure parameters; i.e., the quasiparticle thermal current can reach the critical current. Such a thermophase can be several orders of magnitude larger than that predicted to occur in conventional Josephson tunnel junctions. In order to assess experimentally the predicted very large thermophase, we propose a realistic setup realizable with state-of-the-art nanofabrication techniques and well-established materials, based on a superconducting quantum interference device. This effect could be of strong relevance in several low-temperature applications, for example, for revealing tiny temperature differences generated by coupling the electromagnetic radiation to one of the superconductors forming the junction. PMID:25723238
Josephson junction in a thin film
Kogan, V. G.; Dobrovitski, V. V.; Clem, J. R.; Mawatari, Yasunori; Mints, R. G.
2001-04-01
The phase difference {phi}(y) for a vortex at a line Josephson junction in a thin film attenuates at large distances as a power law, unlike the case of a bulk junction where it approaches exponentially the constant values at infinities. The field of a Josephson vortex is a superposition of fields of standard Pearl vortices distributed along the junction with the line density {phi}'(y)/2{pi}. We study the integral equation for {phi}(y) and show that the phase is sensitive to the ratio l/{Lambda}, where l={lambda}{sub J}{sup 2}/{lambda}{sub L}, {Lambda}=2{lambda}{sub L}{sup 2}/d, {lambda}{sub L}, and {lambda}{sub J} are the London and Josephson penetration depths, and d is the film thickness. For l<<{Lambda}, the vortex ''core'' of the size l is nearly temperature independent, while the phase ''tail'' scales as l{Lambda}/y{sup 2}={lambda}{sub J}2{lambda}{sub L}/d/y{sup 2}; i.e., it diverges as T{yields}T{sub c}. For l>>{Lambda}, both the core and the tail have nearly the same characteristic length l{Lambda}.
Controllable 0-π Josephson junctions containing a ferromagnetic spin valve
NASA Astrophysics Data System (ADS)
Gingrich, E. C.; Niedzielski, Bethany M.; Glick, Joseph A.; Wang, Yixing; Miller, D. L.; Loloee, Reza; Pratt, W. P., Jr.; Birge, Norman O.
2016-06-01
Superconductivity and ferromagnetism are antagonistic forms of order, and rarely coexist. Many interesting new phenomena occur, however, in hybrid superconducting/ferromagnetic systems. For example, a Josephson junction containing a ferromagnetic material can exhibit an intrinsic phase shift of π in its ground state for certain thicknesses of the material. Such `π-junctions' were first realized experimentally in 2001 (refs ,), and have been proposed as circuit elements for both high-speed classical superconducting computing and for quantum computing. Here we demonstrate experimentally that the phase state of a Josephson junction containing two ferromagnetic layers can be toggled between 0 and π by changing the relative orientation of the two magnetizations. These controllable 0-π junctions have immediate applications in cryogenic memory, where they serve as a necessary component to an ultralow power superconducting computer. Such a fully superconducting computer is estimated to be orders of magnitude more energy-efficient than current semiconductor-based supercomputers. Phase-controllable junctions also open up new possibilities for superconducting circuit elements such as superconducting `programmable logic', where they could function in superconducting analogues to field-programmable gate arrays.
Bursting behaviour in coupled Josephson junctions
NASA Astrophysics Data System (ADS)
Hongray, Thotreithem; Balakrishnan, J.; Dana, Syamal K.
2015-12-01
We report an interesting bow-tie shaped bursting behaviour in a certain parameter regime of two resistive-capacitative shunted Josephson junctions, one in the oscillatory and the other in the excitable mode and coupled together resistively. The burst emerges in both the junctions and they show near-complete synchronization for strong enough couplings. We discuss a possible bifurcation scenario to explain the origin of the burst. An exhaustive study on the parameter space of the system is performed, demarcating the regions of bursting from other solutions.
Bursting behaviour in coupled Josephson junctions.
Hongray, Thotreithem; Balakrishnan, J; Dana, Syamal K
2015-12-01
We report an interesting bow-tie shaped bursting behaviour in a certain parameter regime of two resistive-capacitative shunted Josephson junctions, one in the oscillatory and the other in the excitable mode and coupled together resistively. The burst emerges in both the junctions and they show near-complete synchronization for strong enough couplings. We discuss a possible bifurcation scenario to explain the origin of the burst. An exhaustive study on the parameter space of the system is performed, demarcating the regions of bursting from other solutions. PMID:26723143
Soft nanostructuring of YBCO Josephson junctions by phase separation.
Gustafsson, D; Pettersson, H; Iandolo, B; Olsson, E; Bauch, T; Lombardi, F
2010-12-01
We have developed a new method to fabricate biepitaxial YBa2 Cu3 O7-δ (YBCO) Josephson junctions at the nanoscale, allowing junctions widths down to 100 nm and simultaneously avoiding the typical damage in grain boundary interfaces due to conventional patterning procedures. By using the competition between the superconducting YBCO and the insulating Y2 BaCuO5 phases during film growth, we formed nanometer sized grain boundary junctions in the insulating Y2 BaCuO5 matrix as confirmed by high-resolution transmission electron microscopy. Electrical transport measurements give clear indications that we are close to probing the intrinsic properties of the grain boundaries. PMID:21080664
Edge currents in frustrated Josephson junction ladders
NASA Astrophysics Data System (ADS)
Marques, A. M.; Santos, F. D. R.; Dias, R. G.
2016-09-01
We present a numerical study of quasi-1D frustrated Josephson junction ladders with diagonal couplings and open boundary conditions, in the large capacitance limit. We derive a correspondence between the energy of this Josephson junction ladder and the expectation value of the Hamiltonian of an analogous tight-binding model, and show how the overall superconducting state of the chain is equivalent to the minimum energy state of the tight-binding model in the subspace of one-particle states with uniform density. To satisfy the constraint of uniform density, the superconducting state of the ladder is written as a linear combination of the allowed k-states of the tight-binding model with open boundaries. Above a critical value of the parameter t (ratio between the intra-rung and inter-rung Josephson couplings) the ladder spontaneously develops currents at the edges, which spread to the bulk as t is increased until complete coverage is reached. Above a certain value of t, which varies with ladder size (t = 1 for an infinite-sized ladder), the edge currents are destroyed. The value t = 1 corresponds, in the tight-binding model, to the opening of a gap between two bands. We argue that the disappearance of the edge currents with this gap opening is not coincidental, and that this points to a topological origin for these edge current states.
NASA Astrophysics Data System (ADS)
Konschelle, François; Tokatly, Ilya V.; Bergeret, F. Sebastián
2015-09-01
Due to the spin-orbit coupling (SOC) an electric current flowing in a normal metal or semiconductor can induce a bulk magnetic moment. This effect is known as the Edelstein (EE) or magnetoelectric effect. Similarly, in a bulk superconductor a phase gradient may create a finite spin density. The inverse effect, also known as the spin-galvanic effect, corresponds to the creation of a supercurrent by an equilibrium spin polarization. Here, by exploiting the analogy between a linear-in-momentum SOC and a background SU(2) gauge field, we develop a quasiclassical transport theory to deal with magnetoelectric effects in superconducting structures. For bulk superconductors this approach allows us to easily reproduce and generalize a number of previously known results. For Josephson junctions we establish a direct connection between the inverse EE and the appearance of an anomalous phase shift φ0 in the current-phase relation. In particular we show that φ0 is proportional to the equilibrium spin current in the weak link. We also argue that our results are valid generically, beyond the particular case of linear-in-momentum SOC. The magnetoelectric effects discussed in this study may find applications in the emerging field of coherent spintronics with superconductors.
The critical current of point symmetric Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Monaco, Roberto
2016-06-01
The physics of Josephson tunnel junctions drastically depends on their geometrical configurations. The shape of the junction determines the specific form of the magnetic-field dependence of its Josephson current. Here we address the magnetic diffraction patterns of specially shaped planar Josephson tunnel junctions in the presence of an in-plane magnetic field of arbitrary orientations. We focus on a wide ensemble of junctions whose shape is invariant under point reflection. We analyze the implications of this type of isometry and derive the threshold curves of junctions whose shape is the union or the relative complement of two point symmetric plane figures.
Work fluctuations in bosonic Josephson junctions
NASA Astrophysics Data System (ADS)
Lena, R. G.; Palma, G. M.; De Chiara, G.
2016-05-01
We calculate the first two moments and full probability distribution of the work performed on a system of bosonic particles in a two-mode Bose-Hubbard Hamiltonian when the self-interaction term is varied instantaneously or with a finite-time ramp. In the instantaneous case, we show how the irreversible work scales differently depending on whether the system is driven to the Josephson or Fock regime of the bosonic Josephson junction. In the finite-time case, we use optimal control techniques to substantially decrease the irreversible work to negligible values. Our analysis can be implemented in present-day experiments with ultracold atoms and we show how to relate the work statistics to that of the population imbalance of the two modes.
Pinning-modulated non-collective Josephson-vortex motion in stacked Josephson junctions.
Jin, Y.-D.; Lee, G.-H.; Lee, H.-J.; Bae, M.-H.; Koshelev, A. E.; Pohang Univ. of Science and Technology; Univ. of Illinois
2009-01-01
Josephson vortices in naturally stacked Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} tunneling junctions display rich dynamic behavior that derives from the coexistence of three basic states: static Josephson vortex lattice, coherently moving lattice, and incoherent quasiparticle tunneling state. The rich structure of hysteretic branches observed in the current-voltage characteristics can be understood as combinatorial combinations of these three states which are realized in different junctions and evolve separately with magnetic field and bias current. In particular, the multiple Josephson vortex flow branches at low-bias currents arise from the individual depinning of Josephson vortex rows in each junction.
Ballistic transport in InSb Josephson junctions
NASA Astrophysics Data System (ADS)
Damasco, John Jeffrey; Gill, Stephen; Car, Diana; Bakkers, Erik; Mason, Nadya
We present transport measurements on Josephson junctions consisting of InSb nanowires contacted by Al at various junction lengths. Junction behavior as a function of gate voltage, electric field, and magnetic field is discussed. We show that short junctions behave as 1D quantum wires, exhibiting quantized conductance steps. In addition, we show how Josephson behavior changes as transport evolves from ballistic to diffusive as a function of contact spacing.
Synchronized Switching in a Josephson Junction Crystal
NASA Astrophysics Data System (ADS)
Leib, Martin; Hartmann, Michael J.
2014-06-01
We consider a superconducting coplanar waveguide resonator where the central conductor is interrupted by a series of uniformly spaced Josephson junctions. The device forms an extended medium that is optically nonlinear on the single photon level with normal modes that inherit the full nonlinearity of the junctions but are nonetheless accessible via the resonator ports. For specific plasma frequencies of the junctions, a set of normal modes clusters in a narrow band and eventually becomes entirely degenerate. Upon increasing the intensity of a red detuned drive on these modes, we observe a sharp and synchronized switching from low-occupation quantum states to high-occupation classical fields, accompanied by a pronounced jump from low to high output intensity.
Synchronized switching in a josephson junction crystal.
Leib, Martin; Hartmann, Michael J
2014-06-01
We consider a superconducting coplanar waveguide resonator where the central conductor is interrupted by a series of uniformly spaced Josephson junctions. The device forms an extended medium that is optically nonlinear on the single photon level with normal modes that inherit the full nonlinearity of the junctions but are nonetheless accessible via the resonator ports. For specific plasma frequencies of the junctions, a set of normal modes clusters in a narrow band and eventually becomes entirely degenerate. Upon increasing the intensity of a red detuned drive on these modes, we observe a sharp and synchronized switching from low-occupation quantum states to high-occupation classical fields, accompanied by a pronounced jump from low to high output intensity. PMID:24949766
On Chip Josephson Junction Microwave Switch
NASA Astrophysics Data System (ADS)
Naaman, Ofer; Abutaleb, Mohamed; Kirby, Chris; Rennie, Michael
We report on the design and measurement of a reflective single-pole single-throw microwave switch based on a superconducting circuit containing a single Josephson junction. The device has no internal power dissipation, minimal insertion loss, and is controlled by Φ0-level base-band signals. The data demonstrates the device operation with 2 GHz instantaneous bandwidth centered at 10 GHz and better than 20 dB on/off ratio for input powers up to -100 dBm.
On-chip Josephson junction microwave switch
NASA Astrophysics Data System (ADS)
Naaman, O.; Abutaleb, M. O.; Kirby, C.; Rennie, M.
2016-03-01
The authors report on the design and measurement of a reflective single-pole single-throw microwave switch with no internal power dissipation, based on a superconducting circuit containing a single Josephson junction. The data demonstrate the switch operation with 2 GHz instantaneous bandwidth centered at 10 GHz, low insertion loss, and better than 20 dB on/off ratio. The switch's measured performance agrees well with simulations for input powers up to -100 dBm. An extension of the demonstrated circuit to implement a single-pole double-throw switch is shown in simulation.
NASA Astrophysics Data System (ADS)
Serdyukova, S. I.
2014-07-01
We prove that, in the case of non-periodic (with γ = 1) boundary conditions, the calculation of the current-voltage characteristic (IVC) for a stack of n intrinsic Josephson junctions reduces to solving a system of [( n + 1)/2] non-linear differential equations instead of the n original ones. The current voltage characteristic V( I) has the shape of a hysteresis loop. On the back branch of the loop V( I) decreases to zero rapidly near the breakpoint I b . We succeeded to derive an algorithm determining the approximate breakpoint location and to improve simultaneously the mixed numerical-analytical algorithm of IVC calculation for a stack of Josephson junctions developed by us before. The efficiency of the improved algorithm is shown by the calculations of IVC for stacks consisting of various numbers of intrinsic Josephson junctions.
Dissipation and traversal time in Josephson junctions
Cacciari, Ilaria; Ranfagni, Anedio; Moretti, Paolo
2010-05-01
The various ways of evaluating dissipative effects in macroscopic quantum tunneling are re-examined. The results obtained by using functional integration, while confirming those of previously given treatments, enable a comparison with available experimental results relative to Josephson junctions. A criterion based on the shortening of the semiclassical traversal time tau of the barrier with regard to dissipation can be established, according to which DELTAtau/tau > or approx. N/Q, where Q is the quality factor of the junction and N is a numerical constant of order unity. The best agreement with the experiments is obtained for N=1.11, as it results from a semiempirical analysis based on an increase in the potential barrier caused by dissipative effects.
Fabrication of Niobium Nanobridge Josephson Junctions
NASA Astrophysics Data System (ADS)
Tachiki, T.; Horiguchi, K.; Uchida, T.
2014-05-01
To realize antenna-coupled Josephson detectors for microwave and millimeter-wave radiation, planar-type Nb nanobridge Josephson junctions were fabricated. Nb thin films whose thickness, the root mean square roughness and the critical temperature were 20.0 nm, 0.109 nm and 8.4 K, respectively were deposited using a DC magnetron sputtering at a substrate temperature of 700°C. Nanobridges were obtained from the film using 80-kV electron beam lithography and reactive ion-beam etching in CF4 (90%) + O2 (10%) gases. The minimum bridge area was 65 nm wide and 60 nm long. For the nanobridge whose width and length were less than 110 nm, an I-V characteristic showed resistively-shunted-junction behaviour near the critical temperature. Moreover, Shapiro steps were observed in the nanobridge with microwave irradiation at a frequency of 6 - 30 GHz. The Nb nanobridges can be used as detectors in the antenna-coupled devices.
Josephson current in parallel SFS junctions
NASA Astrophysics Data System (ADS)
Ioselevich, Pavel; Ostrovsky, Pavel; Fominov, Yakov; Feigelman, Mikhail
We study a Josephson junction between superconductors connected by two parallel ferromagnetic arms. If the ferromagnets are fully polarised, supercurrent can only flow via Cooper pair splitting between the differently polarised arms. The disorder-average current is suppressed, but mesoscopic fluctuations lead to a significant typical current. We extract the typical current from a current-current correlator. The current is proportional to sin2 α / 2 , where α is the angle between the polarisations of the two arms, revealing the spin dependence of crossed Andreev reflection. Compared to an SNS device of the same geometry, the typical SFS current is small by a factor determined by the properties of the superconducting leads alone. The current is insensitive to the flux threading the area between the ferromagnetic arms of the junction. However, if the ferromagnetic arms are replaced by metal with magnetic impurities, or partially polarised ferromagnets, the Josephson current starts depending on the flux with a period of h / e , i.e. twice the superconducting flux quantum.
Topological phase transition of a Josephson junction and its dynamics
NASA Astrophysics Data System (ADS)
Hutasoit, Jimmy; Marciani, Marco; Tarasinski, Brian; Beenakker, Carlo
A Josephson junction formed by a superconducting ring interrupted by a semiconductor nanowire can realize a zero-dimensional class D topological superconductor. By coupling the Josephson junction to a ballistic wire and altering the strength of the coupling, one can drive this topological superconductor through a topological phase transition. We study the compressibility of the junction as a probe of the topological phase transition. We also study the dynamics of the phase transition by studying the current pulse injected into the wire.
8 π -periodic Josephson effects in a quantum dot/ quantum spin-Hall josephson junction system
NASA Astrophysics Data System (ADS)
Hui, Hoi-Yin; Sau, Jay
2015-03-01
Josephson junctions made of conventional s-wave superconductors display 2 π periodicity. On the other hand, 4 π -periodic fractional Josephson effect is known to be a characteristic signature of topological superconductors and Majorana fermions [1]. Zhang and Kane have shown that Josephson junctions made of topological superconductors are 8 π -periodic if interaction is used to avoid dissipation [2]. Here we present a general argument for how time-reversal symmetry and Z2 non-trivial topology constrains the Josephson periodicity to be 8 π . We then illustrate this through a microscopic model of a quantum dot in a quantum spin-hall Josephson junction. Work supported by NSF-JQI-PFC, LPS-CMTC and Microsoft Q.
Target attractor tracking of relative phase in Bosonic Josephson junction
NASA Astrophysics Data System (ADS)
Borisenok, Sergey
2016-06-01
The relative phase of Bosonic Josephson junction in the Josephson regime of Bose-Hubbard model is tracked via the target attractor (`synergetic') feedback algorithm with the inter-well coupling parameter presented as a control function. The efficiency of our approach is demonstrated numerically for Gaussian and harmonic types of target phases.
Josephson junction array protected from local noises.
NASA Astrophysics Data System (ADS)
Gladchenko, Sergey; Olaya, David; Dupont-Ferrier, Eva; Doucot, Benoit; Ioffe, Lev; Gershenson, Michael
2009-03-01
We have developed small arrays of Josephson junctions (JJs) that can be viewed as prototypes of superconducting qubits protected from local noises [1]. The array consists of twelve superconducting loops interrupted by four sub-micron JJs. The protected state is realized when each loop is threaded by half of the magnetic flux quantum. It has been observed that the array with the optimized amplitude of quantum fluctuations is protected against magnetic flux variations well beyond linear order, in agreement with theoretical predictions [2]. 1. S. Gladchenko et al., ``Superconducting Nanocircuits for Topologically Protected Qubits'', arXiv:cond-mat/0802.2295, to be published in Nature Physics. 2. L.B. Ioffe and M.V. Feigelman, Phys. Rev. B 66, 224503 (2002); B. Doucot et al., Phys. Rev. B 71, 024505 (2005); B. Doucot and L.B. Ioffe, Phys. Rev. B 76, 214507 (2007).
Josephson Current and Multiple Andreev Reflections in Graphene SNS Junctions
NASA Astrophysics Data System (ADS)
Skachko, Ivan; Du, Xu; Andrei, Eva Y.
2008-03-01
The Josephson Effect and Superconducting Proximity Effect were observed in Superconductor-Graphene-Superconductor (SGS) Josephson junctions with coherence lengths comparable to the distance between the superconducting leads. By comparing the measured temperature and gate dependence of the supercurrent and the proximity induced sub-gap features (multiple Andreev reflections) to theoretical predictions, we find that the diffusive junction model yields close quantitative agreement with the results. This is consistent with the fact that the measured mean free paths in these junctions, 10 ˜ 30 nm, are significantly shorter than the lead separation. We show that all SGS devices reported so far fall in the diffusive junction category.
Vortex depinning in Josephson-junction arrays
NASA Astrophysics Data System (ADS)
Dang, E. K. F.; Györffy, B. L.
1993-02-01
On the basis of a simple model we study the supercurrent-carrying capacity of a planar array of Josephson junctions. In particular we investigate the zero-temperature vortex-depinning current iBc, which is the largest supercurrent in an array containing one extra vortex on top of the ground-state vortex superlattice induced by an external magnetic field f. In the zero-field, f=0, case our results support the tilted-sinusoidal vortex-potential description of previous workers. However, in the fully frustrated, f=1/2 case, a more careful interpretation is required. We find that on the application of a transport current, the resulting vortex motion is not that of the extra vortex moving over a rigid field-induced vortex background. Rather, a vortex belonging to the checkerboard ground-state pattern first crosses over a junction into a neighboring ``empty'' plaquette. Then, the ``extra'' vortex moves to take its place. Our interpretation is based on a linear stability analysis, with the onset of vortex motion being associated with the vanishing of one eigenvalue of the stability matrix. Further applications of the method are suggested.
Studying two-level systems in Josephson junctions with a Josephson junction defect spectrometer
NASA Astrophysics Data System (ADS)
Stoutimore, M. J. A.; Khalil, M. S.; Gladchenko, Sergiy; Simmonds, R. W.; Lobb, C. J.; Osborn, K. D.
2012-02-01
We have fabricated and measured Josephson junction defect spectrometers (JJDSs), which are frequency-tunable, nearly-harmonic oscillators that probe two-level systems (TLSs) in the barrier of a Josephson junction (JJ). A JJDS consists of the JJ under study fabricated with a parallel capacitor and inductor such that it can accommodate a wide range of junction inductances, LJ0, while maintaining an operating frequency, f01, in the range of 4-8 GHz. In this device, the parallel inductance helps the JJ maintain linearity over a wide range of frequencies. This architecture allows for the testing of JJs with a wide range of areas and barrier materials, and in the first devices we have tested Al/AlOx/Al JJs. By applying a magnetic flux bias to tune f01, we detect TLSs in the JJ barrier as splittings in the device spectrum. We will present our results toward identifying and quantifying these TLSs, which are known to cause decoherence in quantum devices that rely on JJs.
Determination of the dissipation in superconducting Josephson junctions
Mugnai, D. Ranfagni, A.; Cacciari, I.
2015-02-07
The results relative to macroscopic quantum tunneling rate, out of the metastable state of Josephson junctions, are examined in view of determining the effect of dissipation. We adopt a simple criterion in accordance to which the effect of dissipation can be evaluated by analyzing the shortening of the semiclassical traversal time of the barrier. In almost all the considered cases, especially those with relatively large capacitance values, the relative time shortening turns out to be about 20% and with a corresponding quality factor Q ≃ 5.5. However, beyond the specific cases here considered, still in the regime of moderate dissipation, the method is applicable also to different situations with different values of the quality factor. The method allows, within the error limits, for a reliable determination of the load resistance R{sub L}, the less accessible quantity in the framework of the resistively and capacitively shunted junction model, provided that the characteristics of the junction (intrinsic capacitance, critical current, and the ratio of the bias current to the critical one) are known with sufficient accuracy.
Effect of surface losses on soliton propagation in Josephson junctions
Davidson, A.; Pedersen, N.F.; Pagano, S.
1986-05-12
We have explored numerically the effects on soliton propagation of a third order damping term in the modified sine-Gordon equation. In Josephson tunnel junctions such a term corresponds physically to quasiparticle losses within the metal electrodes of the junction. We find that this loss term plays the dominant role in determining the shape and stability of the soliton at high velocity.
Josephson junctions in high-T/sub c/ superconductors
Falco, C.M.; Lee, T.W.
1981-01-14
The invention includes a high T/sub c/ Josephson sperconducting junction as well as the method and apparatus which provides the junction by application of a closely controlled and monitored electrical discharge to a microbridge region connecting two portions of a superconducting film.
Conditions for synchronization in Josephson-junction arrays
Chernikov, A.A.; Schmidt, G.
1995-12-31
An effective perturbation theoretical method has been developed to study the dynamics of Josephson Junction series arrays. It is shown that the inclusion of Junction capacitances, often ignored, has a significant impact on synchronization. Comparison of analytic with computational results over a wide range of parameters shows excellent agreement.
Processing of Superconductor-Normal-Superconductor Josephson Edge Junctions
NASA Technical Reports Server (NTRS)
Kleinsasser, A. W.; Barner, J. B.
1997-01-01
The electrical behavior of epitaxial superconductor-normal-superconductor (SNS) Josephson edge junctions is strongly affected by processing conditions. Ex-situ processes, utilizing photoresist and polyimide/photoresist mask layers, are employed for ion milling edges for junctions with Yttrium-Barium-Copper-Oxide (YBCO) electrodes and primarily Co-doped YBCO interlayers.
Effect of current injection into thin-film Josephson junctions
Kogan, V. G.; Mints, R. G.
2014-11-11
New thin-film Josephson junctions have recently been tested in which the current injected into one of the junction banks governs Josephson phenomena. One thus can continuously manage the phase distribution at the junction by changing the injected current. Our method of calculating the distribution of injected currents is also proposed for a half-infinite thin-film strip with source-sink points at arbitrary positions at the film edges. The strip width W is assumed small relative to Λ=2λ2/d;λ is the bulk London penetration depth of the film material and d is the film thickness.
Effect of current injection into thin-film Josephson junctions
Kogan, V. G.; Mints, R. G.
2014-11-11
New thin-film Josephson junctions have recently been tested in which the current injected into one of the junction banks governs Josephson phenomena. One thus can continuously manage the phase distribution at the junction by changing the injected current. Our method of calculating the distribution of injected currents is also proposed for a half-infinite thin-film strip with source-sink points at arbitrary positions at the film edges. The strip width W is assumed small relative to Λ=2λ^{2}/d;λ is the bulk London penetration depth of the film material and d is the film thickness.
Effect of current injection into thin-film Josephson junctions
NASA Astrophysics Data System (ADS)
Kogan, V. G.; Mints, R. G.
2014-11-01
New thin-film Josephson junctions have recently been tested in which the current injected into one of the junction banks governs Josephson phenomena. One thus can continuously manage the phase distribution at the junction by changing the injected current. A method of calculating the distribution of injected currents is proposed for a half-infinite thin-film strip with source-sink points at arbitrary positions at the film edges. The strip width W is assumed small relative to Λ =2 λ2/d ;λ is the bulk London penetration depth of the film material and d is the film thickness.
Macroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions.
Massarotti, D; Pal, A; Rotoli, G; Longobardi, L; Blamire, M G; Tafuri, F
2015-01-01
The interfacial coupling of two materials with different ordered phases, such as a superconductor (S) and a ferromagnet (F), is driving new fundamental physics and innovative applications. For example, the creation of spin-filter Josephson junctions and the demonstration of triplet supercurrents have suggested the potential of a dissipationless version of spintronics based on unconventional superconductivity. Here we demonstrate evidence for active quantum applications of S-F-S junctions, through the observation of macroscopic quantum tunnelling in Josephson junctions with GdN ferromagnetic insulator barriers. We show a clear transition from thermal to quantum regime at a crossover temperature of about 100 mK at zero magnetic field in junctions, which present clear signatures of unconventional superconductivity. Following previous demonstration of passive S-F-S phase shifters in a phase qubit, our result paves the way to the active use of spin filter Josephson systems in quantum hybrid circuits. PMID:26054495
Macroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions
Massarotti, D.; Pal, A.; Rotoli, G.; Longobardi, L.; Blamire, M. G.; Tafuri, F.
2015-01-01
The interfacial coupling of two materials with different ordered phases, such as a superconductor (S) and a ferromagnet (F), is driving new fundamental physics and innovative applications. For example, the creation of spin-filter Josephson junctions and the demonstration of triplet supercurrents have suggested the potential of a dissipationless version of spintronics based on unconventional superconductivity. Here we demonstrate evidence for active quantum applications of S-F-S junctions, through the observation of macroscopic quantum tunnelling in Josephson junctions with GdN ferromagnetic insulator barriers. We show a clear transition from thermal to quantum regime at a crossover temperature of about 100 mK at zero magnetic field in junctions, which present clear signatures of unconventional superconductivity. Following previous demonstration of passive S-F-S phase shifters in a phase qubit, our result paves the way to the active use of spin filter Josephson systems in quantum hybrid circuits. PMID:26054495
Quantum interference in topological insulator Josephson junctions
NASA Astrophysics Data System (ADS)
Song, Juntao; Liu, Haiwen; Liu, Jie; Li, Yu-Xian; Joynt, Robert; Sun, Qing-feng; Xie, X. C.
2016-05-01
Using nonequilibrium Green's functions, we studied numerically the transport properties of a Josephson junction, superconductor-topological insulator-superconductor hybrid system. Our numerical calculation shows first that proximity-induced superconductivity is indeed observed in the edge states of a topological insulator adjoining two superconducting leads and second that the special characteristics of topological insulators endow the edge states with an enhanced proximity effect with a superconductor but do not forbid the bulk states to do the same. In a size-dependent analysis of the local current, it was found that a few residual bulk states can lead to measurable resistance, whereas because these bulk states spread over the whole sample, their contribution to the interference pattern is insignificant when the sample size is in the micrometer range. Based on these numerical results, it is concluded that the apparent disappearance of residual bulk states in the superconducting interference process as described by Hart et al. [Nat. Phys. 10, 638 (2014), 10.1038/nphys3036] is just due to the effects of size: the contribution of the topological edge states outweighs that of the residual bulk states.
Graphene Josephson Junction Single Photon Detector
NASA Astrophysics Data System (ADS)
Walsh, Evan D.; Lee, Gil-Ho; Efetov, Dmitri K.; Heuck, Mikkel; Crossno, Jesse; Taniguchi, Takashi; Watanabe, Kenji; Ohki, Thomas A.; Kim, Philip; Englund, Dirk; Fong, Kin Chung
Single photon detectors (SPDs) have found use across a wide array of applications depending on the wavelength to which they are sensitive. Graphene, because of its linear, gapless dispersion near the Dirac point, has a flat, wide bandwidth absorption that can be enhanced to near 100 % through the use of resonant structures making it a promising candidate for broadband SPDs. Upon absorbing a photon in the optical to mid-infrared range, a small (~10 μm2) sheet of graphene at cryogenic temperatures can experience a significant increase in electronic temperature due to its extremely low heat capacity. At 1550 nm, for example, calculations show that the temperature could rise by as much as 500 %. This temperature increase could be detected with near perfect quantum efficiency by making the graphene the weak link in a Josephson junction (JJ). We present a theoretical model demonstrating that such a graphene JJ SPD could operate at the readily achievable temperature of 3 K with near zero dark count, sub-50 ps timing jitter, and sub-5 ns dead time and report on the progress toward experimentally realizing the device.
Fluxon Dynamics in Elliptic Annular Josephson Junctions
NASA Astrophysics Data System (ADS)
Monaco, Roberto; Mygind, Jesper
2016-04-01
We analyze the dynamics of a magnetic flux quantum (current vortex) trapped in a current-biased long planar elliptic annular Josephson tunnel junction. The system is modeled by a perturbed sine-Gordon equation that determines the spatial and temporal behavior of the phase difference across the tunnel barrier separating the two superconducting electrodes. In the absence of an external magnetic field, the fluxon dynamics in an elliptic annulus does not differ from that of a circular annulus where the stationary fluxon speed merely is determined by the system losses. The interaction between the vortex magnetic moment and a spatially homogeneous in-plane magnetic field gives rise to a tunable periodic non-sinusoidal potential which is strongly dependent on the annulus aspect ratio. We study the escape of the vortex from a well in the tilted potential when the bias current exceeds the depinning current. The smallest depinning current as well as the lowest sensitivity of the annulus to the external field is achieved when the axes ratio is equal to √{2}. The presented extensive numerical results are in good agreement with the findings of the perturbative approach. We also probe the rectifying properties of an asymmetric potential implemented with an egg-shaped annulus formed by two semi-elliptic arcs.
Superconducting qubits with semiconductor nanowire Josephson junctions
NASA Astrophysics Data System (ADS)
Petersson, K. D.; Larsen, T. W.; Kuemmeth, F.; Jespersen, T. S.; Krogstrup, P.; Nygård, J.; Marcus, C. M.
2015-03-01
Superconducting transmon qubits are a promising basis for a scalable quantum information processor. The recent development of semiconducting InAs nanowires with in situ molecular beam epitaxy-grown Al contacts presents new possibilities for building hybrid superconductor/semiconductor devices using precise bottom up fabrication techniques. Here, we take advantage of these high quality materials to develop superconducting qubits with superconductor-normal-superconductor Josephson junctions (JJs) where the normal element is an InAs semiconductor nanowire. We have fabricated transmon qubits in which the conventional Al-Al2O3-Al JJs are replaced by a single gate-tunable nanowire JJ. Using spectroscopy to probe the qubit we observe fluctuations in its level splitting with gate voltage that are consistent with universal conductance fluctuations in the nanowire's normal state conductance. Our gate-tunable nanowire transmons may enable new means of control for large scale qubit architectures and hybrid topological quantum computing schemes. Research supported by Microsoft Station Q, Danish National Research Foundation, Villum Foundation, Lundbeck Foundation and the European Commission.
Ferromagnetic planar Josephson junction with transparent interfaces: a φ junction proposal.
Heim, D M; Pugach, N G; Kupriyanov, M Yu; Goldobin, E; Koelle, D; Kleiner, R
2013-05-29
We calculate the current-phase relation of a planar Josephson junction with a ferromagnetic weak link located on top of a thin normal metal film. Following experimental observations we assume transparent superconductor-ferromagnet interfaces. This provides the best interlayer coupling and a low suppression of the superconducting correlations penetrating from the superconducting electrodes into the ferromagnetic layer. We show that this Josephson junction is a promising candidate for experimental φ junction realization. PMID:23636963
Search for Second-Order Josephson tunneling in SFS Josephson junctions
NASA Astrophysics Data System (ADS)
Frolov, S. M.; Oboznov, V. A.
2005-03-01
SFS (Superconductor-Ferromagnet-Superconductor) Josephson junctions can exhibit transitions between ordinary Josephson (0-junction) tunneling and pi-junction behavior as a function of barrier thickness or temperature. Close to the 0-π crossover at which the first-order Josephson component vanishes, it has been predicted that second-order Josephson tunneling, characterized by a sin(2φ) component in the supercurrent, can dominate. If present, this component can be detected directly by measurements of the current-phase relation and can induce period doubling in the critical current diffraction patterns and generate half-integer Shapiro steps. However, such effects can also arise near the 0-π transition from a distribution of 0-junction and π-junction regions due to a non-uniform ferromagnetic barrier. We compare the results of measurements on junctions with uniform and non-uniform ferromagnetic barriers to determine whether observed second harmonics arise from a microscopic sin(2φ) component or from junction non-uniformity.
Black-Schaffer, Annica M.
2010-04-06
We use a tight-binding Bogoliubov-de Gennes (BdG) formalism to self-consistently calculate the proximity effect, Josephson current, and local density of states in ballistic graphene SNS Josephson junctions. Both short and long junctions, with respect to the superconducting coherence length, are considered, as well as different doping levels of the graphene. We show that self-consistency does not notably change the current-phase relationship derived earlier for short junctions using the non-selfconsistent Dirac-BdG formalism but predict a significantly increased critical current with a stronger junction length dependence. In addition, we show that in junctions with no Fermi level mismatch between the N and S regions superconductivity persists even in the longest junctions we can investigate, indicating a diverging Ginzburg-Landau superconducting coherence length in the normal region.
The SNS Josephson junction with a third terminal
NASA Technical Reports Server (NTRS)
Prans, G. P.; Meissner, H.
1974-01-01
Discussion of the operating characteristics of a three-terminal thin-film SNS Josephson junction whose diameter is much greater than the electron pair coherence length in the N metal. It is shown that a junction of this type is essentially a two-terminal device even though the third terminal of the junction supplies the control current. The mechanism underlying this finding is discussed.
Detection of noise-corrupted sinusoidal signals with Josephson junctions
NASA Astrophysics Data System (ADS)
Filatrella, Giovanni; Pierro, Vincenzo
2010-10-01
We investigate the possibility of exploiting the speed and low noise features of Josephson junctions for detecting sinusoidal signals masked by Gaussian noise. We show that the escape time from the static locked state of a Josephson junction is very sensitive to a small periodic signal embedded in the noise, and therefore the analysis of the escape times can be employed to reveal the presence of the sinusoidal component. We propose and characterize two detection strategies: in the first, the initial phase is supposedly unknown (incoherent strategy), while in the second, the signal phase remains unknown but is fixed (coherent strategy). Our proposals are both suboptimal, with the linear filter being the optimal detection strategy, but they present some remarkable features, such as resonant activation, that make detection through Josephson junctions appealing in some special cases.
NASA Astrophysics Data System (ADS)
Serdyukova, S. I.
2013-05-01
We prove that in the case of periodic and nonperiodic (with γ = 0) boundary conditions, the calculation of the current-voltage characteristic for a stack of n intrinsic Josephson junctions reduces to solving a unique equation. The current-voltage characteristic V( I) has the shape of a hysteresis loop. On the back branch of the loop, V( I) rapidly decreases to zero near the breakpoint I b . We succeeded to derive an equation determining the approximate breakpoint location.
Study of charge-phase diagrams for coupled system of Josephson junctions
NASA Astrophysics Data System (ADS)
Hamdipour, M.; Shukrinov, Y. U. M.
2010-11-01
Dynamics of stacked intrinsic Josephson junctions (IJJ) in the high-Tc superconductors is theoretically investigated. We calculate the current-voltage characteristics (CVC) of IJJ and study the breakpoint region on the outermost branch of the CVC for the stacks with 9 IJJ. A method for investigation of the fine structure in CVC of IJJ based on the recording the "phase-charge" diagrams is suggested. It is demonstrated that this method reflects the main features of the breakpoint region.
Observation of short ballistic Josephson effect in vertical graphene junctions
NASA Astrophysics Data System (ADS)
Lee, Gil-Ho; Lee, Hu-Jong
2014-03-01
The current-phase relation (CPR) of vertical graphene Josephson junctions (vGJJs) was measured using phase-sensitive dc-SQUID interferometry. A vGJJ, realized by vertically sandwiching a monolayer graphene between two Al electrodes, had an atomically short channel with transparent contacts for the highly coherent junction nature. The measured CPR was almost perfectly skewed, which rigorously confirmed the short ballisticity of the vGJJs. The short ballistic character of a Josephson junction has been predicted since 1970's but has never been realized in scalable hybrid systems. The CPR also provided energy spectrum of Andreev levels formed inside the junction, which offered a promising prospect for scalable quantum information devices such as Andreev-level qubits. This vertical-junction scheme is also readily applicable to the other cleavable materials such as three-dimensional topological insulators or transition metal dichalcogenides, opening a new pathway for uncovering exotic coherence phenomena arising in an atomic scale.
Building of tridimensional Josephson junction arrays with controlled anisotropy
NASA Astrophysics Data System (ADS)
Passos, Wagner de A. C.; Lima, Emerson de; Ortiz, Wilson A.
2004-08-01
This work depicts optimized preparation routes employed to produce and characterize tridimensional disordered Josephson junction arrays. The arrays were fabricated from granular superconductors, using Nb powder. All relevant signatures of a Josephson junction array are exhibited by the samples, including the typical Fraunhofer dependence of the critical current with the applied magnetic field, a magnetic remanence presented in a certain temperature interval, and the paramagnetic Meissner effect. Our results show that the anisotropy of the samples can be controlled by the pressure applied in the preparation process.
Suspended InAs nanowire Josephson junctions assembled via dielectrophoresis
NASA Astrophysics Data System (ADS)
Montemurro, D.; Stornaiuolo, D.; Massarotti, D.; Ercolani, D.; Sorba, L.; Beltram, F.; Tafuri, F.; Roddaro, S.
2015-09-01
We present a novel technique for the realization of suspended Josephson junctions based on InAs semiconductor nanowires. The devices are assembled using a technique of drop-casting guided by dielectrophoresis, which allows one to finely align the nanostructures on top of the electrodes. The proposed architecture removes the interaction between the nanowire and the substrate which is known to influence disorder and the orientation of the Rashba vector. The relevance of this approach in view of the implementation of hybrid Josephson junctions based on semiconducting nanowires coupled with high-temperature superconductors is discussed.
Suspended InAs nanowire Josephson junctions assembled via dielectrophoresis.
Montemurro, D; Stornaiuolo, D; Massarotti, D; Ercolani, D; Sorba, L; Beltram, F; Tafuri, F; Roddaro, S
2015-09-25
We present a novel technique for the realization of suspended Josephson junctions based on InAs semiconductor nanowires. The devices are assembled using a technique of drop-casting guided by dielectrophoresis, which allows one to finely align the nanostructures on top of the electrodes. The proposed architecture removes the interaction between the nanowire and the substrate which is known to influence disorder and the orientation of the Rashba vector. The relevance of this approach in view of the implementation of hybrid Josephson junctions based on semiconducting nanowires coupled with high-temperature superconductors is discussed. PMID:26335273
Sign reversal of ac Josephson current in a ferromagnetic Josephson junction
NASA Astrophysics Data System (ADS)
Hikino, Shin-Ichi; Mori, Michiyasu; Takahashi, Saburo; Maekawa, Sadamichi
2009-03-01
It is known that in a superconductor/insulator/superconductor (SIS) junction, when a finite voltage is applied, the Josephson current shows a logarithmic divergence, i.e., the so-called Riedel peak(RP) at the gap voltage, V=2δ/e, (δ is a superconducting gap). In a double barrier Josephson junction such as SXS junction, on the other hand, the voltage dependence of Ic has not been investigated so far, where X is a normal metal (N) or a ferromagnet (F). We study the voltage dependence of Josephson critical current (Ic) in a variety of SXS junctions. In a SNS junction, Ic shows the RP at the gap voltage similar to a SIS junction. On the other hand, in a SFS junction, Ic shows a damped oscillation with the alternation of sign as a function of thickness (d) of F due to 0-π transition. The RP exhibits a strong dependence on d, and changes its sign. It is predicted that the RP disappears at the 0-π transition in the SFS junction.
Josephson radiation from InSb-nanowire junction
NASA Astrophysics Data System (ADS)
van Woerkom, David; Proutski, Alexander; Krivachy, Tamas; Bouman, Daniel; van Gulik, Ruben; Gul, Onder; Cassidy, Maja; Car, Diana; Bakkers, Erik; Kouwenhoven, Leo; Geresdi, Attila
Semiconducting nanowire Josephson junctions has recently gained interest as building blocks for Majorana circuits and gate-tuneable superconducting qubits . Here we investigate the rich physics of the Andreev bound state spectrum of InSb nanowire junctions utilizing the AC Josephson relation 2eV_bias =hf . We designed and characterized an on-chip microwave circuit coupling the nanowire junction to an Al/AlOx/Al tunnel junction. The DC response of the tunnel junction is affected by photon-assisted quasiparticle current, which gives us the possibility to measure the radiation spectrum of the nanowire junction up to several tens of GHz in frequency. Our circuit design allows for voltage or phase biasing of the Josephson junction enabling direct mapping of Andreev bound states. We discuss our fabrication methods and choice of materials to achieve radiation detection up to a magnetic field of few hundred milliTesla, compatible with Majorana states in spin-orbit coupled nanowires. This work has been supported by the Netherlands Foundations FOM, Abstract NWO and Microsoft Corporation Station Q.
Thin-film Josephson junctions with alternating critical current density
NASA Astrophysics Data System (ADS)
Moshe, Maayan; Kogan, V. G.; Mints, R. G.
2009-01-01
We study the field dependence of the maximum current Im(H) in narrow edge-type thin-film Josephson junctions with alternating critical current density. Im(H) is evaluated within nonlocal Josephson electrodynamics taking into account the stray fields that affect the difference of the order-parameter phases across the junction and therefore the tunneling currents. We find that the phase difference along the junction is proportional to the applied field, depends on the junction geometry, but is independent of the Josephson critical current density gc , i.e., it is universal. An explicit form for this universal function is derived for small currents through junctions of the width W≪Λ , the Pearl length. The result is used to calculate Im(H) . It is shown that the maxima of Im(H)∝1/H and the zeros of Im(H) are equidistant but only in high fields. We find that the spacing between zeros is proportional to 1/W2 . The general approach is applied to calculate Im(H) for a superconducting quantum interference device with two narrow edge-type junctions. If gc changes sign periodically or randomly, as it does in grain boundaries of high- Tc materials and superconductor-ferromagnet-superconductor heterostructures, Im(H) not only acquires the major side peaks, but due to nonlocality the following peaks decay much slower than in bulk junctions.
Josephson junctions with tunable current-phase relation
NASA Astrophysics Data System (ADS)
Lipman, A.; Mints, R. G.; Kleiner, R.; Koelle, D.; Goldobin, E.
2014-11-01
We consider 0-π Josephson junctions consisting of 0 and π regions of lengths L0 and Lπ with critical current densities jc 0 and jc π, respectively. The dependence of the Josephson current on the phase-shift averaged along the junction is derived. We show that these systems exhibit the main features of φ Josephson junctions—the ground state is doubly degenerate and the current-phase relation can be tuned in situ by applying magnetic field. In the limit of short and long 0 and π regions, the current phase relation is derived analytically. In the case of intermediate lengths of 0 and π regions, the current-phase relation is calculated numerically.
Evidence for Nonlocal Electrodynamics in Planar Josephson Junctions
NASA Astrophysics Data System (ADS)
Boris, A. A.; Rydh, A.; Golod, T.; Motzkau, H.; Klushin, A. M.; Krasnov, V. M.
2013-09-01
We study the temperature dependence of the critical current modulation Ic(H) for two types of planar Josephson junctions: a low-Tc Nb/CuNi/Nb and a high-Tc YBa2Cu3O7-δ bicrystal grain-boundary junction. At low T both junctions exhibit a conventional behavior, described by the local sine-Gordon equation. However, at elevated T the behavior becomes qualitatively different: the Ic(H) modulation field ΔH becomes almost T independent and neither ΔH nor the critical field for the penetration of Josephson vortices vanish at Tc. Such an unusual behavior is in good agreement with theoretical predictions for junctions with nonlocal electrodynamics. We extract absolute values of the London penetration depth λ from our data and show that a crossover from local to nonlocal electrodynamics occurs with increasing T when λ(T) becomes larger than the electrode thickness.
Nonlinear microwave absorption in weak-link Josephson junctions
Xie, L.M.; Wosik, J.; Wolfe, J.C.
1996-12-01
A model, based on the resistively shunted junction theory, is developed and used to study microwave absorption in weak-link Josephson junctions in high-{ital T}{sub {ital c}} superconductors. Both linear and nonlinear cases of microwave absorption in Josephson junctions are analyzed. A comparison of the model with microwave absorption loop theory is presented along with a general condition for the applicability of both models. The nonlinear case was solved numerically and the threshold points of sharp microwave absorption are presented. At these points, a 2{pi} phase quantization takes place within each microwave cycle, leading to an onset of a sharp rise of absorption. Existence of the 2{pi} dynamic quantization is the key to the interpretation of nonlinear microwave absorption data. The nonlinear microwave absorption model is extended to the study of nonuniformly coupled junctions, and a general statement for the applicability of such a model is presented. {copyright} {ital 1996 The American Physical Society.}
Tight-binding study of bilayer graphene Josephson junctions
NASA Astrophysics Data System (ADS)
Muñoz, W. A.; Covaci, L.; Peeters, F. M.
2012-11-01
Using highly efficient simulations of the tight-binding Bogoliubov-de-Gennes model, we solved self-consistently for the pair correlation and the Josephson current in a superconducting-bilayer graphene-superconducting Josephson junction. Different doping levels for the non-superconducting link are considered in the short- and long-junction regimes. Self-consistent results for the pair correlation and superconducting current resemble those reported previously for single-layer graphene except at the Dirac point, where remarkable differences in the proximity effect are found, as well as a suppression of the superconducting current in the long-junction regime. Inversion symmetry is broken by considering a potential difference between the layers and we found that the supercurrent can be switched if the junction length is larger than the Fermi length.
Josephson junction through a disordered topological insulator with helical magnetization
NASA Astrophysics Data System (ADS)
Zyuzin, Alexander; Alidoust, Mohammad; Loss, Daniel
2016-06-01
We study supercurrent and proximity vortices in a Josephson junction made of disordered surface states of a three-dimensional topological insulator with a proximity induced in-plane helical magnetization. In a regime where the rotation period of helical magnetization is larger than the junction width, we find supercurrent 0 -π crossovers as a function of junction thickness, magnetization strength, and parameters inherent to the helical modulation and surface states. The supercurrent reversals are associated with proximity induced vortices, nucleated along the junction width, where the number of vortices and their locations can be manipulated by means of the superconducting phase difference and the parameters mentioned above.
Automatic recording of direct current singularity amplitudes in Josephson junctions
Costabile, G.; Gambardella, U.; Pagano, S.
1985-08-01
We have designed and tested an electronic circuit to record the amplitude of any current singularity in the current-voltage characteristic of a Josephson tunnel junction. The detection of the peak current occurs only when the junction voltage is within a range that can be centered and narrowed conveniently. We describe the circuit in detail and illustrate its operation in the recording of some typical dc singularities.
Nonsinusoidal Current-Phase Relation in SFS Josephson Junctions
NASA Astrophysics Data System (ADS)
Golubov, A. A.; Kupriyanov, M. Yu.; Fominov, Ya. V.
2002-06-01
Various types of the current-phase relation I(phi) in superconductor-ferromagnet-superconductor (SFS) point contacts and planar double-barrier junctions are studied within the quasiclassical theory in the limit of thin diffusive ferromagnetic interlayers. The physical mechanisms leading to highly nontrivial I(phi) dependence are identified by studying the spectral supercurrent density. These mechanisms are also responsible for the 0-pi transition in SFS Josephson junctions.
Evidence for a minigap in YBCO grain boundary Josephson junctions.
Lucignano, P; Stornaiuolo, D; Tafuri, F; Altshuler, B L; Tagliacozzo, A
2010-10-01
Self-assembled YBaCuO diffusive grain boundary submicron Josephson junctions offer a realization of a special regime of the proximity effect, where normal state coherence prevails on the superconducting coherence in the barrier region. Resistance oscillations from the current-voltage characteristic encode mesoscopic information on the junction and more specifically on the minigap induced in the barrier. Their persistence at large voltages is evidence of the long lifetime of the antinodal (high energy) quasiparticles. PMID:21230860
Optical switching in a superconductor-semiconductor-superconductor Josephson junction
NASA Astrophysics Data System (ADS)
Bastian, G.; Göbel, E. O.; Schmitz, J.; Walther, M.; Wagner, J.
1999-07-01
We have fabricated Josephson junctions with a two-dimensional electron gas based on InAs/AlSb/GaSb as the barrier. The behavior of the junction during and after illumination with different wavelengths was studied. Due to a persistent positive and negative photoeffect, depending on the excitation wavelength, the carrier density and hence the critical current as well as the normal resistance could be switched between two different stable states.
Fabrication and Tunneling Properties of Niobium/lead Josephson Junctions
NASA Astrophysics Data System (ADS)
Celaschi, Sergio
High quality Josephson tunneling junctions have been fabricated by the process of electron beam evaporation of the Nb base electrode. Thermal oxidation of Nb coated and uncoated surfaces was used in order to grow the oxide barrier at room temperature. Lead was used to complete the sandwich-type structure. The tunneling properties were profoundly sensitive to the surface properties of the Nb films. We found markedly improved Josephson tunneling characteristics by depositing much higher residual resistance ratio (>100) films which in this case seemed to be single crystal. One of the main deterrents for the practical use of high quality Nb/Nb:O(,X)/Pb Josephson junctions has been the high value of the specific capacitance of the native oxides which is drastically reduced by using single crystal Nb thin films. Some of the important parameters of the junctions can be modified by coating the Nb surface. We have demonstrated that Zr, Ti, and Al can be employed as oxidized barriers on single-crystal Nb films to produce high quality Josephson junctions which preserve the low values of the dielectric constant.
NASA Astrophysics Data System (ADS)
Ramos, Roberto; Carabello, Steve; Lambert, Joseph; Mlack, Jerome; Dai, Wenqing; Shen, Yi.; Li, Qi; Cunnane, Daniel; Zhuang, C. G.; Chen, Ke; Xi, X. X.
2012-02-01
The Josephson junction is an experimental testbed widely used to study resonant activation and macroscopic quantum tunneling. These phenomena have been observed in junctions based on conventional low-temperature superconductors such as Nb and Al, and even in high-Tc, intrinsic superconductors. We report results of superconducting-to normal state switching experiments below 1 K using MgB2-based Josephson heterojunctions with Pb and Nb counter-electrodes. Measurements were made with and without RF excitation. With microwaves, we see evidence of a resonant peak, in addition to the primary escape (from ground state) peak -- consistent with resonant activation. We also observe features suggestive of macroscopic quantum tunneling including peaks in the escape rate enhancements and an ``elbow'' in the graph of calculated escape temperatures Tesc versus sample temperature.
Dynamics of Majorana states in a topological Josephson junction.
Houzet, Manuel; Meyer, Julia S; Badiane, Driss M; Glazman, Leonid I
2013-07-26
Topological Josephson junctions carry 4π-periodic bound states. A finite bias applied to the junction limits the lifetime of the bound state by dynamically coupling it to the continuum. Another characteristic time scale, the phase adjustment time, is determined by the resistance of the circuit "seen" by the junction. We show that the 4π periodicity manifests itself by an even-odd effect in Shapiro steps only if the phase adjustment time is shorter than the lifetime of the bound state. The presence of a peak in the current noise spectrum at half the Josephson frequency is a more robust manifestation of the 4π periodicity, as it persists for an arbitrarily long phase adjustment time. We specify, in terms of the circuit parameters, the conditions necessary for observing the manifestations of 4π periodicity in the noise spectrum and Shapiro step measurements. PMID:23931386
Josephson ϕ0-junction in nanowire quantum dots
NASA Astrophysics Data System (ADS)
Szombati, D. B.; Nadj-Perge, S.; Car, D.; Plissard, S. R.; Bakkers, E. P. A. M.; Kouwenhoven, L. P.
2016-06-01
The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference ϕ between the leads. In the presence of chiral and time-reversal symmetry of the Cooper pair tunnelling process, the current is strictly zero when ϕ vanishes. Only if these underlying symmetries are broken can the supercurrent for ϕ = 0 be finite. This corresponds to a ground state of the junction being offset by a phase ϕ0, different from 0 or π. Here, we report such a Josephson ϕ0-junction based on a nanowire quantum dot. We use a quantum interferometer device to investigate phase offsets and demonstrate that ϕ0 can be controlled by electrostatic gating. Our results may have far-reaching implications for superconducting flux- and phase-defined quantum bits as well as for exploring topological superconductivity in quantum dot systems.
Mesoscopic Josephson junctions with switchable current-phase relation
NASA Astrophysics Data System (ADS)
Strambini, E.; Bergeret, F. S.; Giazotto, F.
2015-10-01
We propose and analyze a mesoscopic Josephson junction consisting of two ferromagnetic insulator-superconductors (FI-Ss) coupled through a normal metal (N) layer. The Josephson current of the junction is non-trivially affected by the spin-splitting field induced by the FIs in the two superconductors. In particular, it shows sizeable enhancement by increasing the amplitude of the exchange field (hex) and displays a switchable current-phase relation which depends on the relative orientation of h ex in the FIs. In a realistic EuS/Al-based setup this junction can be exploited as a high-resolution threshold sensor for the magnetic field as well as an on-demand tunable kinetic inductor.
Josephson current and multiple Andreev reflections in graphene SNS junctions
NASA Astrophysics Data System (ADS)
Du, Xu; Skachko, Ivan; Andrei, Eva Y.
2008-05-01
The Josephson effect and superconducting proximity effect were observed in superconductor-graphene-superconductor (SGS) Josephson junctions with coherence lengths comparable to the distance between the superconducting leads. By comparing the measured gate dependence of the proximity induced subgap features (multiple Andreev reflections) and of the supercurrent to theoretical predictions, we find that the diffusive junction model yields close quantitative agreement with the results. By contrast, predictions of the ballistic SGS model are inconsistent with the data. We show that all SGS devices reported so far, our own as well as those of other groups, fall in the diffusive junction category. This is attributed to substrate induced potential fluctuations due to trapped charges and to the invasiveness of the metallic leads.
Triplet supercurrent in ferromagnetic Josephson junctions by spin injection
NASA Astrophysics Data System (ADS)
Mal'shukov, A. G.; Brataas, Arne
2012-09-01
We show that injecting nonequilibrium spins into the superconducting leads strongly enhances the stationary Josephson current through a superconductor-ferromagnet-superconductor junction. The resulting long-range supercurrent through a ferromagnet is carried by triplet Cooper pairs that are formed in s-wave superconductors by the combined effects of spin injection and exchange interaction. We quantify the exchange interaction in terms of Landau Fermi-liquid factors. The magnitude and direction of the long-range Josephson current can be manipulated by varying the angles of the injected polarizations with respect to the magnetization in the ferromagnet.
Scanning SQUID microscopy of SFS π-Josephson junction arrays
NASA Astrophysics Data System (ADS)
Stoutimore, M. J. A.; Oboznov, V. A.
2005-03-01
We use a Scanning SQUID Microscope to image the magnetic flux distribution in arrays of SFS (superconductor-ferromagnet-superconductor) Josephson junctions. The junctions are fabricated with barrier thickness such that they undergo a transition to a π-junction state at a temperature Tπ 2-4 K. In arrays with cells that have an odd number of π-junctions, we observe spontaneously generated magnetic flux in zero applied magnetic field. We image both fully-frustrated arrays and arrays with non-uniform frustration created by varying the number of π-junctions in the cells. By monitoring the onset of spontaneous flux as a function of temperature near Tπ,^ we estimate the uniformity of the junction critical currents.
Cleland, A.N.
1991-04-01
Experiments investigating the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very small capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters; the tunneling rate in the moderately damped (Q {approx} 1) junction is seen to be reduced by a factor of 300 from that predicted for an undamped junction. The phase is seen to be a good quantum-mechanical variable. The experiments on small capacitance tunnel junctions extend the measurements on the larger-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wavefunction has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias. I present the first clear observation of the Coulomb blockade in single junctions. The electrical environment of the tunnel junction, however, strongly affects the behavior of the junction: higher resistance leads are observed to greatly sharpen the Coulomb blockade over that seen with lower resistance leads. I present theoretical descriptions of how the environment influences the junctions; comparisons with the experimental results are in reasonable agreement.
Quantum Phase Slips in Topological Josephson Junction Rings
NASA Astrophysics Data System (ADS)
Rodriguez Mota, Rosa; Vishveshwara, Smitha; Pereg-Barnea, Tami
We study quantum phase slip processes (QPS) in a ring of N topological superconducting islands joined by Josephson junctions and threaded by magnetic flux. In this array, neighboring islands interact through the usual charge 2e Josephson tunneling and the Majorana assisted charge e tunneling. When the charging energy associated with the island's capacitance is zero, the energy vs. flux relation of the system is characterized by parabolas centered around even or odd multiples of the superconducting flux quantum, depending on the parity of the system. For small but non-zero charging energy, quantum fluctuations can lead to tunneling between these classical states. In this work, we calculate the amplitude of these tunneling processes, commonly known as quantum phase slips. We also add gate voltages to our system and study how the amplitude of QPS in these topological Josephson array is modified by Aharanov-Casher interference effects.
Cooper pair splitting in parallel quantum dot Josephson junctions
Deacon, R. S.; Oiwa, A.; Sailer, J.; Baba, S.; Kanai, Y.; Shibata, K.; Hirakawa, K.; Tarucha, S.
2015-01-01
Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair. PMID:26130172
Possible resonance effect of axionic dark matter in Josephson junctions.
Beck, Christian
2013-12-01
We provide theoretical arguments that dark-matter axions from the galactic halo that pass through Earth may generate a small observable signal in resonant S/N/S Josephson junctions. The corresponding interaction process is based on the uniqueness of the gauge-invariant axion Josephson phase angle modulo 2π and is predicted to produce a small Shapiro steplike feature without externally applied microwave radiation when the Josephson frequency resonates with the axion mass. A resonance signal of so far unknown origin observed by C. Hoffmann et al. [Phys. Rev. B 70, 180503(R) (2004)] is consistent with our theory and can be interpreted in terms of an axion mass m(a)c2=0.11 meV and a local galactic axionic dark-matter density of 0.05 GeV/cm3. We discuss future experimental checks to confirm the dark-matter nature of the observed signal. PMID:24476255
Cooper pair splitting in parallel quantum dot Josephson junctions.
Deacon, R S; Oiwa, A; Sailer, J; Baba, S; Kanai, Y; Shibata, K; Hirakawa, K; Tarucha, S
2015-01-01
Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair. PMID:26130172
Josephson Coupling in Nb/SmB6/Nb Junctions
NASA Astrophysics Data System (ADS)
Zhang, Xiaohang; Lee, Seunghun; Drisko, Jasper; Cumings, John; Greene, Richard; Takeuchi, Ichiro
Josephson coupling of superconductors through a topological surface has attracted considerable attention because it may provide device applications of topological insulators with implications for Majorana fermions. However, the results of previous Josephson junction studies on topological insulators have not been fully understood due to complications arising from the conducting bulk and the non-pristine nature of the surfaces/interfaces of the topological insulator materials used. In this work, SmB6 thin films with a highly insulating bulk were adopted to minimize the influence of the bulk carriers while in-situ deposition of Nb film on SmB6 surface was used to ensure the interface quality. The bilayer structure was then patterned into Nb/SmB6/Nb lateral junctions by e-beam lithography and ion milling. The Nb electrodes in our junctions had a typical width of ~1 μm and the gap between the two Nb electrodes was varied from 50 nm to 200 nm. A critical current up to 40 μA has been observed in junctions with a gap around 50 nm at 2.0 K. In this talk, I will discuss the implication of our results to the desired Josephson coupling through topological surface states. This work was supported by NSF under Grant No. DMR-1410665 and conducted at CNAM and at the Maryland NanoCenter.
Supercurrent reversal in Josephson junctions based on bilayer graphene flakes
NASA Astrophysics Data System (ADS)
Rameshti, Babak Zare; Zareyan, Malek; Moghaddam, Ali G.
2015-08-01
We investigate the Josephson effect in a bilayer graphene flake contacted by two monolayer sheets deposited by superconducting electrodes. It is found that when the electrodes are attached to the different layers of the bilayer, the Josephson current is in a π state, if the bilayer region is undoped and there is no vertical bias. Applying doping or bias to the junction reveals π -0 transitions which can be controlled by varying the temperature and the junction length. The supercurrent reversal here is very different from the ferromagnetic Josephson junctions where the spin degree of freedom plays the key role. We argue that the scattering processes accompanied by layer and sublattice index change give rise to the scattering phases, the effect of which varies with doping and bias. Such scattering phases are responsible for the π -0 transitions. On the other hand, if both of the electrodes are coupled to the same layer of the flake or the flake has AA stacking instead of common AB, the junction will be always in 0 state since the layer or sublattice index is not changed.
Measurement of Quantum Phase-Slips in Josephson Junction Chains
NASA Astrophysics Data System (ADS)
Guichard, Wiebke
2011-03-01
Quantum phase-slip dynamics in Josephson junction chains could provide the basis for the realization of a new type of topologically protected qubit or for the implementation of a new current standard. I will present measurements of the effect of quantum phase-slips on the ground state of a Josephson junction chain. We can tune in situ the strength of the phase-slips. These phase-slips are the result of fluctuations induced by the finite charging energy of each junction in the chain. Our measurements demonstrate that a Josephson junction chain under phase bias constraint behaves in a collective way. I will also show evidence of coherent phase-slip interference, the so called Aharonov-Casher effect. This phenomenon is the dual of the well known Aharonov-Bohm interference. In collaboration with I.M. Pop, Institut Neel, C.N.R.S. and Universite Joseph Fourier, BP 166, 38042 Grenoble, France; I. Protopopov, L. D. Landau Institute for Theoretical Physics, Kosygin str. 2, Moscow 119334, Russia and Institut fuer Nanotechnologie, Karlsruher Institut fuer Technologie, 76021 Karlsruhe, Germany; and F. Lecocq, Z. Peng, B. Pannetier, O. Buisson, Institut Neel, C.N.R.S. and Universite Joseph Fourier. European STREP MIDAS, ANR QUANTJO.
Effects of the environment on the switching current in graphene-based Josephson Junctions
NASA Astrophysics Data System (ADS)
Borzenets, Ivan; Ke, Chung-Ting; Amet, Francois; Tso Wei, Ming; Yamamoto, Michihisa; Bomze, Yuriy; Tarucha, Seigo; Finkelstein, Gleb
The nature of the switching current and hysteresis (difference between switching and retrapping currents) in graphene-based Josephson junctions depends greatly on the interaction with the environment. Conventional devices result in underdamped Josephson junctions making the true critical current inaccessible. On the other hand, heavily isolating the Josephson junctions places them in the microscopic quantum tunneling regime even at high temperatures, also masking the critical current. We study the critical current, and the switching statistics in graphene Josephson junctions while varying the effects of the environment. Proper isolation of graphene Josephson junctions is necessary to measure the true critical current, especially so for the cases of small currents around the Dirac point. This is true for the case of conventional diffusive as well as the novel ballistic Josephson junctions.
Intrinsic reduction of Josephson critical current in short ballistic SNS weak links
NASA Astrophysics Data System (ADS)
Nikolić, Branislav K.; Freericks, J. K.; Miller, P.
2001-12-01
We present fully self-consistent calculations of the thermodynamic properties of three-dimensional clean SNS Josephson junctions, where S is an s-wave short-coherence-length superconductor and N is a clean normal metal. The junction is modeled on an infinite cubic lattice such that the transverse width of the S is the same as that of the N, and its thickness is tuned from the short to long limit. Intrinsic effects, such as a reduced order parameter near the SN boundary and finite gap to Fermi energy ratio, depress the critical Josephson current Ic, even in short junctions. Our analysis is of relevance to experiments on SNS junctions which find much smaller IcRN products than expected from the standard (non-self-consistent and quasiclassical) predictions. We also find nonstandard current-phase relations, a counterintuitive spatial distribution of the self-consistently determined order parameter phase, and an unusual low-energy gap in the local density of states within the N region.
Quasi-optical Josephson-junction oscillator arrays
NASA Technical Reports Server (NTRS)
Stern, J. A.; Leduc, H. G.; Zmuidzinas, J.
1993-01-01
Josephson junctions are natural voltage-controlled oscillators capable of generating submillimeter-wavelength radiation, but a single junction usually can produce only 100 nW of power and often has a broad spectral linewidth. The authors are investigating 2D quasi-optical power combining arrays of 103 and 104 NbN/MgO/NbN and Nb/Al-AlO(x)/Nb junctions to overcome these limitations. The junctions are dc-biased in parallel and are distributed along interdigitated lines. The arrays couple to a resonant mode of a Fabry-Perot cavity to achieve mutual phase-locking. The array configuration has a relatively low impedance, which should allow the capacitance of the junctions to be tuned out at the oscillation frequency.
Critical Current Oscillations of Josephson Junctions with Ferromagnetic Layers
NASA Astrophysics Data System (ADS)
Glick, Joseph A.; Khasawneh, Mazin A.; Niedzielski, Bethany M.; Loloee, Reza; Pratt, W. P., Jr.; Birge, Norman O.
Josephson junctions containing ferromagnetic layers are of considerable interest for the development of practical cryogenic memory and superconducting qubits. Such junctions exhibit a phase shift of π for certain ranges of ferromagnetic layer thickness. We present studies of Nb based micron-scale Josephson junctions using ferromagnetic layers of Ni, Ni81Fe19, or Ni65Co20Fe15. By applying an external magnetic field, the critical current of the junctions containing Ni81Fe19 and Ni65Co20Fe15 is found to follow a characteristic Fraunhofer pattern, and displays the clear switching behavior expected of single-domain magnets. However, the junctions containing Ni exhibit more complex behaviors. The maximum value of the critical current, extracted from the Fraunhofer patterns, oscillates as a function of the ferromagnetic layer thickness, indicating transitions in the phase difference across the junction between values of zero and π. We compare the data to previous work and to models of the 0- π transitions based on existing clean and dirty limit theories. This work was supported by IARPA via ARO Contract W911NF-14-C-0115.
Dissipation in a simple model of a topological Josephson junction.
Matthews, Paul; Ribeiro, Pedro; García-García, Antonio M
2014-06-20
The topological features of low-dimensional superconductors have created a lot of excitement recently because of their broad range of applications in quantum information and their potential to reveal novel phases of quantum matter. A potential problem for practical applications is the presence of phase slips that break phase coherence. Dissipation in nontopological superconductors suppresses phase slips and can restore long-range order. Here, we investigate the role of dissipation in a topological Josephson junction. We show that the combined effects of topology and dissipation keep phase and antiphase slips strongly correlated so that the device is superconducting even under conditions where a nontopological device would be resistive. The resistive transition occurs at a critical value of the dissipation that is 4 times smaller than that expected for a conventional Josephson junction. We propose that this difference could be employed as a robust experimental signature of topological superconductivity. PMID:24996102
Semiclassical Quantization of Spinning Quasiparticles in Ballistic Josephson Junctions.
Konschelle, François; Bergeret, F Sebastián; Tokatly, Ilya V
2016-06-10
A Josephson junction made of a generic magnetic material sandwiched between two conventional superconductors is studied in the ballistic semiclassic limit. The spectrum of Andreev bound states is obtained from the single valuedness of a particle-hole spinor over closed orbits generated by electron-hole reflections at the interfaces between superconducting and normal materials. The semiclassical quantization condition is shown to depend only on the angle mismatch between initial and final spin directions along such closed trajectories. For the demonstration, an Andreev-Wilson loop in the composite position-particle-hole-spin space is constructed and shown to depend on only two parameters, namely, a magnetic phase shift and a local precession axis for the spin. The details of the Andreev-Wilson loop can be extracted via measuring the spin-resolved density of states. A Josephson junction can thus be viewed as an analog computer of closed-path-ordered exponentials. PMID:27341251
Semiclassical Quantization of Spinning Quasiparticles in Ballistic Josephson Junctions
NASA Astrophysics Data System (ADS)
Konschelle, François; Bergeret, F. Sebastián; Tokatly, Ilya V.
2016-06-01
A Josephson junction made of a generic magnetic material sandwiched between two conventional superconductors is studied in the ballistic semiclassic limit. The spectrum of Andreev bound states is obtained from the single valuedness of a particle-hole spinor over closed orbits generated by electron-hole reflections at the interfaces between superconducting and normal materials. The semiclassical quantization condition is shown to depend only on the angle mismatch between initial and final spin directions along such closed trajectories. For the demonstration, an Andreev-Wilson loop in the composite position-particle-hole-spin space is constructed and shown to depend on only two parameters, namely, a magnetic phase shift and a local precession axis for the spin. The details of the Andreev-Wilson loop can be extracted via measuring the spin-resolved density of states. A Josephson junction can thus be viewed as an analog computer of closed-path-ordered exponentials.
Interference effect on a Josephson junction with magnetic interfaces
NASA Astrophysics Data System (ADS)
Choi, Chi-Hoon
2013-05-01
We study the proximity effect in a superconductor-normal-superconductor (SNS) layer with spin-active interfaces, paying particular attention to the effect of interference on the transition between 0 and π states of a Josephson junction. We compute the supercurrent density in the ballistic limit by using the Green's function formalism without making the quasiclassical approximation to study the interference effect due to coherent scattering of quasiparticles from the interfaces. The supercurrent is strongly influenced by various factors such as the thickness of the normal layer, the strength of the interface potential, and the orientation of the interface spin. We also discuss the symmetry of the induced superconducting pair amplitude for the 0 and the π states. The detailed features of the effect of interference on the Josephson junction can be important for applications of quantum devices.
Electron Transport Through Josephson Junction Containing a Dimeric Structure
NASA Astrophysics Data System (ADS)
Val'kov, V. V.; Aksenov, S. V.
2016-02-01
The dc Josephson effect in a superconductor/dimeric molecule/superconductor junction has been investigated by means of the nonequilibrium Green's function method and the Keldysh diagram technique. The application of the atomic representation has allowed to simplify considerably the computation of the supercurrent and occupation numbers and receive the general expressions which take into account all processes of the Andreev reflection in the loopless approach. It is significant that the expressions for the current and occupation numbers are valid for different multilevel structures in the Josephson junction. The sf-exchange interaction between the electron spin and the spins of the dimer leads to the suppression of the critical current due to a new set of Andreev bound states.
Dissipation in a Simple Model of a Topological Josephson Junction
NASA Astrophysics Data System (ADS)
Matthews, Paul; Ribeiro, Pedro; García-García, Antonio M.
2014-06-01
The topological features of low-dimensional superconductors have created a lot of excitement recently because of their broad range of applications in quantum information and their potential to reveal novel phases of quantum matter. A potential problem for practical applications is the presence of phase slips that break phase coherence. Dissipation in nontopological superconductors suppresses phase slips and can restore long-range order. Here, we investigate the role of dissipation in a topological Josephson junction. We show that the combined effects of topology and dissipation keep phase and antiphase slips strongly correlated so that the device is superconducting even under conditions where a nontopological device would be resistive. The resistive transition occurs at a critical value of the dissipation that is 4 times smaller than that expected for a conventional Josephson junction. We propose that this difference could be employed as a robust experimental signature of topological superconductivity.
Josephson supercurrent in a graphene-superconductor junction
NASA Astrophysics Data System (ADS)
Sarvestani, E.; Jafari, S. A.
2012-01-01
Within the tunneling Hamiltonian formulation for the eight-component spinors, the Josephson critical supercurrent has been calculated in a planar superconductor-normal graphene-superconductor junction. Coupling between superconductor regions and graphene is taken into account by a tunneling Hamiltonian which contains two types of tunneling, intravalley and intervalley tunneling. Within the present tunneling approach, we find that the contributions of two kinds of tunneling to the critical supercurrent are completely separable. Therefore, it is possible to consider the effect of the intervalley tunnelings in the critical supercurrent. The incorporation of these type of processes into the tunneling Hamiltonian exposes a special feature of the graphene Josephson junctions. The effect of intervalley tunneling appears in the length dependence plot of critical current in the form of oscillations. We also present the results for temperature dependence of critical supercurrent and compare with experimental results and other theoretical calculations.
NASA Astrophysics Data System (ADS)
Black-Schaffer, Annica; Doniach, Sebastian
2008-03-01
Using the self-consistent tight-binding Bogoliubov-de Gennes (BdG) formalism, we investigate the proximity effect and current-phase relationship in SNS graphene Josephson junctions. Both short and long junctions are considered, as well as different doping levels of the graphene. For short junctions at zero doping in the uncorrelated regime our results agree with those found using the non self-consistent Dirac-BdG formalism [1]. We introduce electronic correlations in the Hamiltonian by including the intrinsic nearest-neighbor spin-singlet coupling present in p π-bonded planar organic molecules. We study the possibility of coupling this intrinsic s- or d-wave superconducting pairing [2] to the extrinsic s-wave order parameter induced by the metal electrodes. The intrinsic d-wave solution, favored in doped graphene, appears for longer doped junctions. For short junctions, the s-wave solution can occur, although the result is sensitive to the type of interface. We also report on the two different intrinsic superconducting states' influence on the supercurrent. [1] M. Titov et al. PRB 74 041401 (2006) [2] A. Black-Schaffer et al. PRB 75 134512 (2007)
Collective effects in the two-dimensional Josephson junction array
NASA Astrophysics Data System (ADS)
Vinokour, Valerii; Sadovskyy, Ivan; Galda, Alexey
2013-03-01
We study collective quantum effects in the two-dimensional Josephson junction arrays (JJA) in the vicinity of the superconductor-insulator transition (SIT). We find the contribution of the quantum coherent phase slips (QCPS) into the formation of thermodynamic properties of the JJA, including critical current, as a function of the magnetic field. We investigate the response of the 2D JJA to the external bias and the contribution from QCPS to this response.
A travelling-wave parametric amplifier utilizing Josephson junctions
Sweeny, M.; Mahler, R.
1985-03-01
Josephson junction parametric amplifiers of travelling-wave design have been designed for use as low-noise millimeter wave amplifiers. These devices have non-reciprocal gain, very wide bandwidths, power dissipations of a few tens of nanowatts, and an input impedance that can be as high as 50 ohms. The design is described and performance estimates, based on a small-signal model, are summarized.
Search for a correlation between Josephson junctions and gravity
NASA Astrophysics Data System (ADS)
Robertson, Glen A.
2000-01-01
Woodward's transient mass shift (TMS) formula has commonality with Modanese's anomalous coupling theory (ACT) and Woodward's capacitor experiment has commonality with Podkletnov's layered superconductor disk experiment. The TMS formula derives a mass fluctuation from a time-varying energy density. The ACT suggests that the essential ingredient for the gravity phenomenon is the presence of strong variations or fluctuations of the Cooper pair density (a time-varying energy density). Woodward's experiment used a small array of capacitors whose energy density was varied by an applied 11 kHz signal. Podkletnov's superconductor disk contained many Josephson junctions (small capacitive like interfaces), which were radiated with a 3-4 MHz signal. This paper formulates a TMS for superconductor Josephson junctions. The equation was compared to the 2% mass change claimed by Podkletnov in his gravity shielding experiments. The TMS is calculated to be 2% for a 2-kg superconductor with an induced total power to the multiple Josephson junctions of about 3.3-watts. A percent mass change equation is then formulated based on the Cavendish balance equation where the superconductor TMS is used for the delta change in mass. An experiment using a Cavendish balance is then discussed. .
Fabrication and measurement of multi-terminal mesoscopic Josephson junctions
NASA Astrophysics Data System (ADS)
Solovyeva, Natalya; Tetsuya, Mishima; Santos, Michael; Shabani, Javad; Manucharyan, Vladimir
We present fabrication and characterization of 3- and 4-terminal mesoscopic Josephson junctions involving InAs quantum well heterostructures and superconducting Al contacts. A cross-shaped nanowire junction region with dimensions of order a few 100 nm is dry-etched in the 2DEG, followed by deposition of superconducting contacts and gating electrodes. These novel 0D devices have been recently predicted to have topological features in their Andreev spectra and finite-bias transport; they may also be useful in efforts towards observation and braiding of Majorana fermions in the solid state. // This material is based upon work supported by the NSF under Grant No. DMR-1207537.
Magnetic resonance in a singlet-triplet Josephson junction
NASA Astrophysics Data System (ADS)
Elster, Lars; Houzet, Manuel; Meyer, Julia S.
2016-03-01
We study a singlet-triplet Josephson junction between a conventional s -wave superconductor and an unconventional px-wave superconductor. The Andreev spectrum of the junction yields a spontaneous magnetization in equilibrium. This allows manipulating the occupation of the Andreev levels using an ac Zeeman field. The induced Rabi oscillations manifest themselves as a resonance in the current-phase relation. For a circularly polarized magnetic field, we find a spin selection rule, yielding Rabi oscillations only in a certain interval of the superconducting phase difference.
Positive moment of an inductively coupled Josephson-junction array
Chandran, M.
1997-09-01
We present the results of a Langevin dynamic simulation of an inductively coupled Josephson-junction array in the absence of {pi} junctions. The magnetic susceptibility (4{pi}{chi}) under field-cooled conditions becomes positive in certain range of applied field (f) in antithesis to the Meissner effect, whereas the zero-field cooled susceptibility is negative for all values of f. The results are discussed in the light of recent experiments showing a paramagnetic Meissner effect in certain granular superconductors. {copyright} {ital 1997} {ital The American Physical Society}
Spin-triplet supercurrent in planar geometry ferromagnetic Josephson junctions
NASA Astrophysics Data System (ADS)
Martinez, William M.; Pratt, W. P., Jr.; Birge, Norman O.
2013-03-01
The spin-triplet supercurrent in ferromagnetic Josephson junctions is obtained by surrounding the central ferromagnet with noncollinear ferromagnetic layers, F'. In metallic ferromagnets, the long-range nature of the spin-triplet supercurrent has only been tested to lengths of a few tens of nm. In this work, we are fabricating and measuring S/F'/F/F'/S junctions where the central F layer has a lateral geometry with lengths up to a few hundred nm. We will report on our recent progress. Supported by the DOE under grant DE-FG-02-06ER46341.
Thin Films and Josephson Junctions of Yttrium Barium Copper Oxide
NASA Astrophysics Data System (ADS)
Rosenthal, Peter Andrew
We have studied the growth of superconducting films of rm Y_1Ba_2Cu_3O _{7-delta} using reactive electron beam coevaporation. Emphasis was placed on determining the most important growth parameters, and optimizing the instrumentation for controlling the growth environment. We have experimented with atomic absorption based deposition rate control, quartz lamp based substrate heating, and various forms of activated oxygen. Methods for generating and delivering molecular oxygen, oxygen ion beams, ozone and atomic oxygen were investigated and their effects on film quality were characterized. We found that the specific method of oxidation was not critical to the film quality but that optimal films were produced at lower pressures (~10^{-4} T) for more chemically reactive allotropes of oxygen. Composition was found to be quite important in determining the film properties. These results are discussed in the context of growth kinetics and equilibrium thermodynamics. We have studied the transport properties of artificial grain boundary Josephson junctions of rm Y_1Ba_2Cu_3O_{7-delta }. Measurements and modeling of the magnetic interference patterns of the critical currents revealed the presence of extensive disorder within the junctions. The temperature dependence of the critical currents revealed behavior consistent with the resistively shunted junction (RSJ) model. Modeling the inhomogeneous junctions as parallel arrays of RSJ-like junctions explained the clean RSJ-like current-voltage characteristics even in junctions showing extremely complicated magnetic interference patterns. The observed modulation period of the single junction interference patterns showed an unusual w^{-2} width dependence that could be quantitatively explained by a model of flux focusing based on the London theory. A model of the diffraction patterns for junctions fabricated from extremely thin films shows unexpected deviations from the usual behavior. These peculiarities are understood in terms of
Manipulating Josephson junctions in thin-films by nearby vortices
Kogan, V G; Mints, R G
2014-07-01
It is shown that a vortex trapped in one of the banks of a planar edge-type Josephson junction in a narrow thin-film superconducting strip can change drastically the dependence of the junction critical current on the applied field, I-c(H). When the vortex is placed at certain discrete positions in the strip middle, the pattern I-c(H) has zero at H = 0 instead of the traditional maximum of '0-type' junctions. The number of these positions is equal to the number of vortices trapped at the same location. When the junction-vortex separation exceeds similar to W, the strip width, I-c(H) is no longer sensitive to the vortex presence. The same is true for any separation if the vortex approaches the strip edges. (C) 2014 Elsevier B.V. All rights reserved.
The in-phase states of Josephson junctions stacks as attractors
Hristov, I.; Dimova, S.; Hristova, R.
2014-11-12
The aim of this investigation is to show that the coherent, in-phase states of intrinsic Josephson junctions stacks are attractors of the stacks' states when the applied external magnetic field h{sub e} and the external current γ vary within certain domains. Mathematically the problem is to find the solutions of the system of perturbed sine-Gordon equations for fixed other parameters and zero or random initial conditions. We determine the region in the plane (h{sub e}, γ), where the in-phase states are attractors of the stack's states for arbitrary initial perturbations. This is important, because the in-phase states are required for achieving terahertz radiation from the Josephson stacks.
An IR focal plane array employing superconducting Josephson junction thermal detectors
NASA Astrophysics Data System (ADS)
Osterman, D. P.; Yao, C.-T.; Dang, H.; Cohen, C.; Radparvar, M.
1990-07-01
Thin-film superconductors invite the single-process/single-substrate fabrication of IR detector arrays and their associated processing circuitry. In place of the bolometric thermal-detection principle typical of previous superconductor-employing schemes, the temperature-dependence of the current-voltage relation in a current-biased Josephson tunnel junction is used in the present device; this yields very low intrinsic detector noise, as well as clearly-defined 'on' and 'off' states. Superconducting processing circuitry encompassing addressing and decoding circuits, analog amplifiers, and ADC has been tested for an 8 x 8 prototype array.
Fluctuation of heat current in Josephson junctions
Virtanen, P.; Giazotto, F.
2015-02-15
We discuss the statistics of heat current between two superconductors at different temperatures connected by a generic weak link. As the electronic heat in superconductors is carried by Bogoliubov quasiparticles, the heat transport fluctuations follow the Levitov–Lesovik relation. We identify the energy-dependent quasiparticle transmission probabilities and discuss the resulting probability density and fluctuation relations of the heat current. We consider multichannel junctions, and find that heat transport in diffusive junctions is unique in that its statistics is independent of the phase difference between the superconductors.
High quality ferromagnetic 0 and π Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Weides, M.; Kemmler, M.; Goldobin, E.; Koelle, D.; Kleiner, R.; Kohlstedt, H.; Buzdin, A.
2006-09-01
The authors fabricated high quality Nb /Al2O3/Ni0.6Cu0.4/Nb superconductor-insulatorferromagnet-superconductor Josephson tunnel junctions. Depending on the thickness of the ferromagnetic Ni0.6Cu0.4 layer and on the ambient temperature, the junctions were in the 0 or π ground state. All junctions have homogeneous interfaces showing almost perfect Fraunhofer patterns. The Al2O3 tunnel barrier allows one to achieve rather low damping, which is desired for many experiments especially in the quantum domain. The McCumber parameter βc increases exponentially with decreasing temperature and reaches βc≈700 at T =2.11K. The critical current density in the π state was up to 5A/cm2 at T =2.11K, resulting in a Josephson penetration depth λJ as low as 160μm. Experimentally determined junction parameters are well described by theory taking into account spin-flip scattering in the Ni0.6Cu0.4 layer and different transparencies of the interfaces.
Noise performance of superconductive magnetometers based on long Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Granata, Carmine; Vettoliere, Antonio; Monaco, Roberto
2014-09-01
The low-current fluctuations at cryogenic temperatures together with the low dynamical resistance in the resonant states of Josephson tunnel junctions allow for the realization of superconducting oscillators up to the THz range with ultra-low spectral linewidth. By virtue of the Josephson frequency-voltage relationship, we show that the same properties can be exploited for the practical realization of magnetic flux-to-voltage transducers based on the flux-flow in long Josephson tunnel junctions whose intrinsic low-frequency voltage fluctuations at 4.2\\;K amount to few pV/H{{z}^{1/2}}, that is, too small to be measured by any present semiconductor electronics. Nevertheless, by using a double transformer SQUID amplifier we demonstrate that the (amplitude) voltage spectral density, S_{V}^{1/2}, of an all-niobium sensor does not exceed the level of 10\\;pV/H{{z}^{1/2}} and is not affected by 1/f excess noise at least down to few hertz. Such ultra-low white noise, corresponding to a magnetic field noise S_{B}^{1/2}\\leqslant 10\\;fT/H{{z}^{1/2}}, together with a highly linear and broadband voltage responsivity over a wide magnetic flux range, makes the flux-flow magnetometers potentially competitive with SQUID-based devices.
High-Tc SNS Junctions: A New Generation of Proximity-Coupled Josephson Devices
NASA Technical Reports Server (NTRS)
Kleinsasser, A. W.
1997-01-01
This paper reviews this evolution of proximity - coupled Josephson jucntion from the early investigations on low temperature superconductor-normal -superconductor junctions through the introduction of hybrid superconductor-semiconductor devices and the resulting interest in mesoscopic Josephson junctions, to the recent development of high temperature devices.
Magnesium diboride josephson junctions for superconducting devices and circuits
NASA Astrophysics Data System (ADS)
Cunnane, Daniel
Superconductivity in magnesium diboride (MgB2) was first discovered in 2001. It is unique in that it has two superconducting gaps. The transition temperature of 39 K exceeded the maximum transition temperature thought to be possible through phonon mediated superconductivity. Through the study of MgB2, a general paradigm is being formulated to describe multi-gap superconductors. The paradigm includes inter-band and intra-band scattering between the gaps which can cause a smearing of the gap parameter over a distribution instead of a single value. Although each gap is individually thought to be well described by the BCS theory, the interaction between the two gaps causes complications in describing the overall superconducting properties of MgB2. The focus of this work was to lay the groundwork for an MgB2-based Josephson junction technology. This includes improving on a previously established baseline for all-MgB2 Josephson junctions, utilizing the Josephson Effect to experimentally verify a model pertaining to the two-gap nature of MgB2, specifically the magnetic penetration depth, and designing, fabricating, and testing multi-junction devices and circuits. The experiments in this work included fabrication of Josephson Junctions, DC superconducting quantum interference devices (SQUIDs), Josephson junction arrays, and a rapid single flux quantum (RSFQ) circuit. The junctions were all made utilizing the hybrid physical-chemical vapor deposition method, with an MgO sputtered barrier. The current process consists of three superconducting layers which are patterned using standard UV photolithography and etched with Ar ion milling. There were SQUIDS made with sensitivity to magnetic fields parallel to the film surface, which were used to measure the inductance of MgB2 microstrips. This inductance was used in design of more complicated devices as well as in calculating the magnetic penetration depth of MgB2, found to be about 40 nm at low temperature, in good agreement
Tunable ground states in helical p-wave Josephson junctions
NASA Astrophysics Data System (ADS)
Cheng, Qiang; Zhang, Kunhua; Yu, Dongyang; Chen, Chongju; Zhang, Yinhan; Jin, Biao
2016-07-01
We study new types of Josephson junctions composed of helical p-wave superconductors with {k}x\\hat{x}+/- {k}y\\hat{y} and {k}y\\hat{x}+/- {k}x\\hat{y}-pairing symmetries using quasi-classical Green’s functions with generalized Riccati parametrization. The junctions can host rich ground states: π phase, 0 + π phase, φ 0 phase and φ phase. The phase transition can be tuned by rotating the magnetization in the ferromagnetic interface. We present the phase diagrams in the parameter space formed by the orientation of the magnetization or by the magnitude of the interfacial potentials. The selection rules for the lowest order current which are responsible for the formation of the rich phases are summarized from the current-phase relations based on the numerical calculation. We construct a Ginzburg–Landau type of free energy for the junctions with d-vectors and the magnetization, which not only reveals the interaction forms of spin-triplet superconductivity and ferromagnetism, but can also directly lead to the selection rules. In addition, the energies of the Andreev bound states and the novel symmetries in the current-phase relations are also investigated. Our results are helpful both in the prediction of novel Josephson phases and in the design of quantum circuits.
Detecting evidence for chiral superconductivity in Sr2RuO4 through the use of Josephson junctions
NASA Astrophysics Data System (ADS)
Zakrzewski, Brian; Ying, Y. A.; Cai, Xinxin; Mills, Shaun; Staley, N. E.; Xin, Y.; Fobes, David; Liu, Tijiang; Mao, Zhi-Qiang; Liu, Ying
Sr2RuO4 is predicted to be an odd-parity, spin-triplet superconductor, possibly featuring a doubly degenerate chiral order parameter, which leads to the presence of chiral edge currents, domains, and domain walls. We fabricated Josephson junctions on ramps cut by focused ion beam as well as on naturally cleaved edges of micron thick crystals of Sr2RuO4 using Al as the conventional superconductor electrode. The sensitivity of these Josephson junctions to a magnetic flux penetrating the junction and the domain dependent intrinsic phase of the superconducting order parameter make them a powerful tool for probing the effects of chiral superconductivity mentioned above. We will present the methodology as well as preliminary measurements and discuss the implications of our results.
Characterization of anomalous pair currents in Josephson junction networks.
Ottaviani, I; Lucci, M; Menditto, R; Merlo, V; Salvato, M; Cirillo, M; Müller, F; Weimann, T; Castellano, M G; Chiarello, F; Torrioli, G; Russo, R
2014-05-28
Measurements performed on superconductive networks shaped in the form of planar graphs display anomalously large currents when specific branches are biased. The temperature dependences of these currents evidence that their origin is due to Cooper pair hopping through the Josephson junctions connecting the superconductive islands of the array. The experimental data are discussed in terms of theoretical models which predict, for the system under consideration, an inhomogeneous Cooper pair distribution on the superconductive islands of the network as a consequence of a Bose-Einstein condensation phenomenon. PMID:24787550
Resonant phase matching of Josephson junction traveling wave parametric amplifiers.
O'Brien, Kevin; Macklin, Chris; Siddiqi, Irfan; Zhang, Xiang
2014-10-10
We propose a technique to overcome phase mismatch in Josephson-junction traveling wave parametric amplifiers in order to achieve high gain over a broad bandwidth. Using "resonant phase matching," we design a compact superconducting device consisting of a transmission line with subwavelength resonant inclusions that simultaneously achieves a gain of 20 dB, an instantaneous bandwidth of 3 GHz, and a saturation power of -98 dBm. Such an amplifier is well suited to cryogenic broadband microwave measurements such as the multiplexed readout of quantum coherent circuits based on superconducting, semiconducting, or nanomechanical elements, as well as traditional astronomical detectors. PMID:25375734
Resonant Phase Matching of Josephson Junction Traveling Wave Parametric Amplifiers
NASA Astrophysics Data System (ADS)
O'Brien, Kevin; Macklin, Chris; Siddiqi, Irfan; Zhang, Xiang
2014-10-01
We propose a technique to overcome phase mismatch in Josephson-junction traveling wave parametric amplifiers in order to achieve high gain over a broad bandwidth. Using "resonant phase matching," we design a compact superconducting device consisting of a transmission line with subwavelength resonant inclusions that simultaneously achieves a gain of 20 dB, an instantaneous bandwidth of 3 GHz, and a saturation power of -98 dBm. Such an amplifier is well suited to cryogenic broadband microwave measurements such as the multiplexed readout of quantum coherent circuits based on superconducting, semiconducting, or nanomechanical elements, as well as traditional astronomical detectors.
Crises in a driven Josephson junction studied by cell mapping
Soerensen, M.P.; Davidson, A.; Pedersen, N.F.; Pagano, S.
1988-11-15
We use the method of cell-to-cell mapping to locate attractors, basins, and saddle nodes in the phase plane of a driven Josephson junction. The cell-mapping method is discussed in some detail, emphasizing its ability to provide a global view of the phase plane. Our computations confirm the existence of a previously reported interior crisis. In addition, we observe a boundary crisis for a small shift in one parameter. The cell-mapping method allows us to show both crises explicitly in the phase plane, at low computational cost.
Quantum impurities: from mobile Josephson junctions to depletons
NASA Astrophysics Data System (ADS)
Schecter, Michael; Gangardt, Dimitri M.; Kamenev, Alex
2016-06-01
We overview the main features of mobile impurities moving in one-dimensional superfluid backgrounds by modeling it as a mobile Josephson junction, which leads naturally to the periodic dispersion of the impurity. The dissipation processes, such as radiative friction and quantum viscosity, are shown to result from the interaction of the collective phase difference with the background phonons. We develop a more realistic depleton model of an impurity-hole bound state that provides a number of exact results interpolating between the semiclassical weakly interacting picture and the strongly interacting Tonks–Girardeau regime. We also discuss the physics of a trapped impurity, relevant to current experiments with ultra cold atoms.
Phase diffusion in graphene-based Josephson junctions.
Borzenets, I V; Coskun, U C; Jones, S J; Finkelstein, G
2011-09-23
We report on graphene-based Josephson junctions with contacts made from lead. The high transition temperature of this superconductor allows us to observe the supercurrent branch at temperatures up to ∼2 K, at which point we can detect a small, but nonzero, resistance. We attribute this resistance to the phase diffusion mechanism, which has not been yet identified in graphene. By measuring the resistance as a function of temperature and gate voltage, we can further characterize the nature of the electromagnetic environment and dissipation in our samples. PMID:22026894
Phase Diffusion in Graphene-Based Josephson Junctions
NASA Astrophysics Data System (ADS)
Borzenets, I. V.; Coskun, U. C.; Jones, S. J.; Finkelstein, G.
2011-09-01
We report on graphene-based Josephson junctions with contacts made from lead. The high transition temperature of this superconductor allows us to observe the supercurrent branch at temperatures up to ˜2K, at which point we can detect a small, but nonzero, resistance. We attribute this resistance to the phase diffusion mechanism, which has not been yet identified in graphene. By measuring the resistance as a function of temperature and gate voltage, we can further characterize the nature of the electromagnetic environment and dissipation in our samples.
Precise Heater Controller with rf-Biased Josephson Junctions
NASA Technical Reports Server (NTRS)
Green, Colin J.; Sergatskov, Dmitri A.; Duncan, R. V.
2003-01-01
Paramagnetic susceptibility thermometers used in fundamental physics experiments are capable of measuring temperature changes with a precision of a part in 2 x 10(exp 10). However, heater controllers are only able to control open-loop power dissipation to about a part in 10(exp 5). We used an array of rf-biased Josephson junctions to precisely control the electrical power dissipation in a heater resistor mounted on a thermally isolated cryogenic platform. Theoretically, this method is capable of controlling the electrical power dissipation to better than a part in 10(exp 12). However, this level has not yet been demonstrated experimentally. The experiment consists of a liquid helium cell that also functions as a high-resolution PdMn thermometer, with a heater resistor mounted on it. The cell is thermally connected to a temperature-controlled cooling stage via a weak thermal link. The heater resistor is electrically connected to the array of Josephson junctions using superconducting wire. An rf-biased array of capacitively shunted Josephson junctions drives the voltage across the heater. The quantized voltage across the resistor is Vn = nf(h/2e), where h is Planck's constant, f is the array biasing frequency, e is the charge of an electron, and n is the integer quantum state of the Josephson array. This results in an electrical power dissipation on the cell of Pn = (Vn)(sup 2/R), where R is the heater resistance. The change of the quantum state of the array changes the power dissipated in the heater, which in turn, results in the change of the cell temperature. This temperature change is compared to the expected values based on the known thermal standoff resistance of the cell from the cooling stage. We will present our initial experimental results and discuss future improvements. This work has been funded by the Fundamental Physics Discipline of the Microgravity Science Office of NASA, and supported by a no-cost equipment loan from Sandia National Laboratories.
Multi-terminal Josephson junctions as topological matter
NASA Astrophysics Data System (ADS)
Riwar, Roman-Pascal; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
Topological materials and their unusual transport properties are now at the focus of modern experimental and theoretical research. Their topological properties arise from the bandstructure determined by the atomic composition of a material and as such are difficult to tune and naturally restricted to <= 3 dimensions. Here we demonstrate that n-terminal Josephson junctions with conventional superconductors may provide novel realizations of topology in n - 1 dimensions, which have similarities, but also marked differences with existing 2D or 3D topological materials. For n >= 4 , the Andreev subgap spectrum of the junction can accommodate Weyl singularities in the space of the n - 1 independent superconducting phases, which play the role of bandstructure quasimomenta. The presence of these Weyl singularities enables topological transitions that are manifested experimentally as changes of the quantized transconductance between two voltage-biased leads, the quantization unit being 4e2 / h .
Nonequilibrium work by charge control in a Josephson junction.
Yi, Su Do; Kim, Beom Jun; Yi, Juyeon
2013-08-01
We consider a single Josephson junction in the presence of time varying gate charge, and examine the nonequilibrium work done by the charge control in the framework of fluctuation theorems. Assuming first a high quality junction with negligible Ohmic current, we obtain the probability distribution functions of the work and confirm the Crooks relation to give the estimation of the free energy changes ΔF=0. The reliability of ΔF estimated from the Jarzynksi equality is crucially dependent on protocol parameters, while the Bennett's acceptance ratio method yields consistently ΔF=0. We examine the behaviors of the work average and point out its relation to heat and entropy production associated with the circuit control. Finally considering finite tunnel resistance we discuss dissipation effects on the work statistics. PMID:24032811
Reentrant ac Magnetic Susceptibility in Josephson-Junction Arrays
Araujo-Moreira, F.M.; Barbara, P.; Cawthorne, A.B.; Lobb, C.J.
1997-06-01
We have measured the complex ac magnetic susceptibility of unshunted Josephson-junction arrays as a function of temperature T , amplitude of the excitation field h{sub ac} , and external magnetic field H{sub dc} . For small h{sub ac} Meissner screening occurs. For larger h{sub ac} , however, the screening is reentrant in T . This reentrance is not thermodynamic but dynamic and arises from the paramagnetic contribution of multijunction loops. This result gives an alternative explanation of the paramagnetic Meissner effect observed in granular superconductors. Experimental results are in agreement with a simplified model based on a single loop containing four junctions. {copyright} {ital 1997} {ital The American Physical Society}
Suspended metal mask techniques in Josephson junction fabrication
Ono, R.H.; Sauvageau, J.E.; Jain, A.K.; Schwartz, D.B.; Springer, K.T.; Lukens, J.E.
1985-01-01
We report here two processes for in-situ, self-aligned fabrication of niobium based Josephson tunnel junctions and SNS microbridges in which multiple evaporations at varying angles are made through a suspended metal stencil fabricated by electron beam lithography (EBL). Both techniques have proved superior to earlier all-polymer suspended masks, particularly with e-gun evaporated refractory metals such as niobium. The first process uses a trilevel resist and ion milling to pattern a gold stencil suspended on PMMA. In the second process, an aluminum stencil suspended on polyimide (PI) is patterned by lift-off with an EBL mask written in a PMMA layer on top of the PI. The PI is then undercut using an oxygen plasma etch through the aluminum mask. Reproducible ( +- 20 nm) submicrometer dimensions and good junction characteristics have been achieved using these techniques without the need for difficult-to-control surface cleaning procedures.
Multi-terminal Josephson junctions as topological matter
NASA Astrophysics Data System (ADS)
Riwar, Roman-Pascal; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
2016-04-01
Topological materials and their unusual transport properties are now at the focus of modern experimental and theoretical research. Their topological properties arise from the bandstructure determined by the atomic composition of a material and as such are difficult to tune and naturally restricted to <=3 dimensions. Here we demonstrate that n-terminal Josephson junctions with conventional superconductors may provide novel realizations of topology in n-1 dimensions, which have similarities, but also marked differences with existing 2D or 3D topological materials. For n>=4, the Andreev subgap spectrum of the junction can accommodate Weyl singularities in the space of the n-1 independent superconducting phases, which play the role of bandstructure quasimomenta. The presence of these Weyl singularities enables topological transitions that are manifested experimentally as changes of the quantized transconductance between two voltage-biased leads, the quantization unit being 4e2/h, where e is the electric charge and h is the Planck constant.